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Mathematics
Class 92025–26 SNC28 Questions SolvedEnglish Medium

Exercise 6.1 — Class 9 Mathematics Solutions

All 28 questions below are worked step by step — every step clearly worked out with mathematical reasons — for the Punjab Board 9th class Mathematics textbook.

Exercise 6.1

9 Questions (19 Sub-parts)

Every step explained, with hints and the method used.

Question 1

EasyUnder Review

Find in which quadrant the following angles lie. Write a co-terminal angle for each.

Hint

Locate the terminal side by comparing the angle with the quadrant boundaries, then add or subtract 360∘ to get a co-terminal angle.

Solution

(This question consists of multiple subparts. See solutions below.)

Quick Solution

Q1Part (i)

EasyUnder Review

65∘

Hint

Compare the angle with the boundaries 0∘,±90∘,±180∘,±270∘, then add 360∘.

Solution

  1. Locate the terminal side.

    A positive angle is measured anticlockwise from the positive x-axis. Quadrant I covers angles between 0∘ and 90∘. Its terminal side lies between the positive x-axis and the positive y-axis.

    0∘<65∘<90∘

  2. Name the quadrant.

    So 65∘ lies in Quadrant I.

  3. Write a co-terminal angle.

    Co-terminal angles share the same terminal side, so adding 360∘ (one full turn) gives one.

    65∘+360∘=425∘

Answer

65∘∈Quadrant I,co-terminal angle=425∘

Quick Solution

Q1Part (ii)

EasyUnder Review

135∘

Hint

Compare the angle with the boundaries 0∘,±90∘,±180∘,±270∘, then add 360∘.

Solution

  1. Locate the terminal side.

    A positive angle is measured anticlockwise. Quadrant II covers angles between 90∘ and 180∘. Its terminal side lies between the positive y-axis and the negative x-axis.

    90∘<135∘<180∘

  2. Name the quadrant.

    So 135∘ lies in Quadrant II.

  3. Write a co-terminal angle.

    Co-terminal angles share the same terminal side, so adding 360∘ (one full turn) gives one.

    135∘+360∘=495∘

Answer

135∘∈Quadrant II,co-terminal angle=495∘

Quick Solution

Q1Part (iii)

EasyUnder Review

−40∘

Hint

Compare the angle with the boundaries 0∘,±90∘,±180∘,±270∘, then add 360∘.

Solution

  1. Locate the terminal side.

    A negative angle is measured clockwise from the positive x-axis. Turning clockwise by less than 90∘ lands in Quadrant IV. Its terminal side lies between the positive x-axis and the negative y-axis.

    −90∘<−40∘<0∘

  2. Name the quadrant.

    So −40∘ lies in Quadrant IV.

  3. Write a co-terminal angle.

    Co-terminal angles share the same terminal side, so adding 360∘ (one full turn) gives one.

    −40∘+360∘=320∘

Answer

−40∘∈Quadrant IV,co-terminal angle=320∘

Quick Solution

Q1Part (iv)

EasyUnder Review

210∘

Hint

Compare the angle with the boundaries 0∘,±90∘,±180∘,±270∘, then add 360∘.

Solution

  1. Locate the terminal side.

    A positive angle is measured anticlockwise. Quadrant III covers angles between 180∘ and 270∘. Its terminal side lies between the negative x-axis and the negative y-axis.

    180∘<210∘<270∘

  2. Name the quadrant.

    So 210∘ lies in Quadrant III.

  3. Write a co-terminal angle.

    Co-terminal angles share the same terminal side, so adding 360∘ (one full turn) gives one.

    210∘+360∘=570∘

Answer

210∘∈Quadrant III,co-terminal angle=570∘

Quick Solution

Q1Part (v)

EasyUnder Review

−150∘

Hint

Compare the angle with the boundaries 0∘,±90∘,±180∘,±270∘, then add 360∘.

Solution

  1. Locate the terminal side.

    A negative angle is measured clockwise. Turning clockwise past −90∘ but not past −180∘ lands in Quadrant III. Its terminal side lies between the negative y-axis and the negative x-axis.

    −180∘<−150∘<−90∘

  2. Name the quadrant.

    So −150∘ lies in Quadrant III.

  3. Write a co-terminal angle.

    Co-terminal angles share the same terminal side, so adding 360∘ (one full turn) gives one.

    −150∘+360∘=210∘

Answer

−150∘∈Quadrant III,co-terminal angle=210∘

Quick Solution

Question 2

EasyUnder Review

Convert the following into degrees, minutes and seconds.

Hint

Multiply the decimal part of the degrees by 60 to get minutes, then the decimal part of the minutes by 60 to get seconds.

Solution

(This question consists of multiple subparts. See solutions below.)

Quick Solution

Q2Part (i)

EasyUnder Review

123.456∘

Hint

Use 1∘=60′ and 1′=60′′ on the decimal parts.

Solution

  1. Separate the whole degrees.

    Split the angle into its whole number of degrees and its decimal part.

    123.456∘=123∘+0.456∘
  2. Convert the decimal degrees to minutes.

    Since 1∘=60′, multiply the decimal part by 60.

    0.456∘=(0.456×60)′=27.36′=27′+0.36′
  3. Convert the decimal minutes to seconds.

    Since 1′=60′′, multiply the remaining decimal part by 60.

    0.36′=(0.36×60)′′=21.6′′
  4. Combine.

    Put the degrees, minutes and seconds together.

    123.456∘=123∘27′21.6′′

Answer

123.456∘=123∘27′21.6′′

Quick Solution

Q2Part (ii)

EasyUnder Review

58.7891∘

Hint

Use 1∘=60′ and 1′=60′′ on the decimal parts.

Solution

  1. Separate the whole degrees.

    Split the angle into its whole number of degrees and its decimal part.

    58.7891∘=58∘+0.7891∘
  2. Convert the decimal degrees to minutes.

    Since 1∘=60′, multiply the decimal part by 60.

    0.7891∘=(0.7891×60)′=47.346′=47′+0.346′
  3. Convert the decimal minutes to seconds.

    Since 1′=60′′, multiply the remaining decimal part by 60.

    0.346′=(0.346×60)′′=20.76′′
  4. Combine.

    Put the degrees, minutes and seconds together.

    58.7891∘=58∘47′20.76′′

Answer

58.7891∘=58∘47′20.76′′≈58∘47′21′′

Quick Solution

Q2Part (iii)

EasyUnder Review

90.5678∘

Hint

Use 1∘=60′ and 1′=60′′ on the decimal parts.

Solution

  1. Separate the whole degrees.

    Split the angle into its whole number of degrees and its decimal part.

    90.5678∘=90∘+0.5678∘
  2. Convert the decimal degrees to minutes.

    Since 1∘=60′, multiply the decimal part by 60.

    0.5678∘=(0.5678×60)′=34.068′=34′+0.068′
  3. Convert the decimal minutes to seconds.

    Since 1′=60′′, multiply the remaining decimal part by 60.

    0.068′=(0.068×60)′′=4.08′′
  4. Combine.

    Put the degrees, minutes and seconds together.

    90.5678∘=90∘34′4.08′′

Answer

90.5678∘=90∘34′4.08′′

Quick Solution

Question 3

EasyUnder Review

Convert the following into decimal degrees.

Hint

Divide the minutes by 60 and the seconds by 3600, then add them to the degrees.

Solution

(This question consists of multiple subparts. See solutions below.)

Quick Solution

Q3Part (i)

EasyUnder Review

65∘32′15′′

Hint

Use 1′=160∘ and 1′′=13600∘.

Solution

  1. Convert minutes and seconds to degrees.

    Since 1′=(160)∘ and 1′′=(13600)∘, divide the minutes by 60 and the seconds by 3600.

    32′=(3260)∘=0.5333∘ 15′′=(153600)∘=0.0042∘
  2. Add to the whole degrees.

    Add both decimal parts to the degrees. Keeping the exact fractions, 3260+153600=19353600=0.5375, so the rounded values add correctly.

    65∘32′15′′=65∘+0.5333∘+0.0042∘=65.5375∘

Answer

65∘32′15′′=65.5375∘

Quick Solution

Q3Part (ii)

EasyUnder Review

42∘18′45′′

Hint

Use 1′=160∘ and 1′′=13600∘.

Solution

  1. Convert minutes and seconds to degrees.

    Since 1′=(160)∘ and 1′′=(13600)∘, divide the minutes by 60 and the seconds by 3600.

    18′=(1860)∘=0.3∘ 45′′=(453600)∘=0.0125∘
  2. Add to the whole degrees.

    Add both decimal parts to the degrees.

    42∘18′45′′=42∘+0.3∘+0.0125∘=42.3125∘

Answer

42∘18′45′′=42.3125∘

Quick Solution

Q3Part (iii)

EasyUnder Review

78∘45′36′′

Hint

Use 1′=160∘ and 1′′=13600∘.

Solution

  1. Convert minutes and seconds to degrees.

    Since 1′=(160)∘ and 1′′=(13600)∘, divide the minutes by 60 and the seconds by 3600.

    45′=(4560)∘=0.75∘ 36′′=(363600)∘=0.01∘
  2. Add to the whole degrees.

    Add both decimal parts to the degrees.

    78∘45′36′′=78∘+0.75∘+0.01∘=78.76∘

Answer

78∘45′36′′=78.76∘

Quick Solution

Question 4

EasyUnder Review

Convert the following into radian.

Hint

Multiply the number of degrees by π180 and simplify the fraction.

Solution

(This question consists of multiple subparts. See solutions below.)

Quick Solution

Q4Part (i)

EasyUnder Review

36∘

Hint

Multiply by π180.

Solution

  1. Use the conversion factor.

    Since 180∘=π rad, we have 1∘=π180 rad.

    36∘=36×π180 rad=36π180 rad
  2. Simplify.

    Divide 36 and 180 by their HCF, 36.

    36∘=π5 rad≈0.6283 rad

Answer

36∘=π5 rad≈0.6283 rad

Quick Solution

Q4Part (ii)

EasyUnder Review

22.5∘

Hint

Multiply by π180.

Solution

  1. Use the conversion factor.

    Since 180∘=π rad, we have 1∘=π180 rad.

    22.5∘=22.5×π180 rad=22.5π180 rad
  2. Simplify.

    Since 180÷22.5=8, the fraction reduces to 18.

    22.5∘=π8 rad≈0.3927 rad

Answer

22.5∘=π8 rad≈0.3927 rad

Quick Solution

Q4Part (iii)

EasyUnder Review

67.5∘

Hint

Multiply by π180.

Solution

  1. Use the conversion factor.

    Since 180∘=π rad, we have 1∘=π180 rad.

    67.5∘=67.5×π180 rad=67.5π180 rad
  2. Simplify.

    Since 67.5=3×22.5 and 180=8×22.5, the fraction reduces to 38.

    67.5∘=3π8 rad≈1.1781 rad

Answer

67.5∘=3π8 rad≈1.1781 rad

Quick Solution

Question 5

EasyUnder Review

Convert the following into degrees.

Hint

Multiply the radian measure by 180∘π; the π cancels.

Solution

(This question consists of multiple subparts. See solutions below.)

Quick Solution

Q5Part (i)

EasyUnder Review

π16 rad

Hint

Multiply by 180∘π and cancel π.

Solution

  1. Use the conversion factor.

    Since π rad =180∘, we have 1 rad =180∘π.

    π16 rad=π16×180∘π=180∘16=11.25∘
  2. Express in degrees and minutes.

    Since 0.25∘=15′, this is also 11∘15′.

Answer

π16 rad=11.25∘

Quick Solution

Q5Part (ii)

EasyUnder Review

11π5 rad

Hint

Multiply by 180∘π and cancel π.

Solution

Use the conversion factor.

Since π rad =180∘, we have 1 rad =180∘π.

11π5 rad=11π5×180∘π=11×36∘=396∘

Answer

11π5 rad=396∘

Quick Solution

Q5Part (iii)

EasyUnder Review

7π6 rad

Hint

Multiply by 180∘π and cancel π.

Solution

Use the conversion factor.

Since π rad =180∘, we have 1 rad =180∘π.

7π6 rad=7π6×180∘π=7×30∘=210∘

Answer

7π6 rad=210∘

Quick Solution

Question 6

MediumUnder Review

Find the arc length and area of a sector with:

Hint

Use ℓ=rθ and A=12r2θ with θ in radians.

Solution

(This question consists of multiple subparts. See solutions below.)

Quick Solution

Q6Part (i)

EasyUnder Review

r=6 cm and θ=π3 rad

Hint

Substitute directly into ℓ=rθ and A=12r2θ.

Solution

  1. Find the arc length.

    With θ in radians, the arc length is ℓ=rθ.

    ℓ=6×π3=2π cm≈6.28 cm
  2. Find the area of the sector.

    The area of a sector is A=12r2θ.

    A=12×62×π3=36π6=6π cm2≈18.85 cm2

Answer

ℓ=2π≈6.28 cm,A=6π≈18.85 cm2

Quick Solution

Q6Part (ii)

MediumUnder Review

r=4.8π cm and central angle θ=5π6 radians

Hint

Find ℓ=rθ first, then use A=12rℓ.

Solution

  1. Find the arc length.

    With θ in radians, ℓ=rθ; the π cancels.

    ℓ=4.8π×5π6=246=4 cm
  2. Find the area of the sector.

    Since A=12r2θ=12r(rθ), we can use A=12rℓ with the arc length just found.

    A=12×4.8π×4=9.6π cm2≈3.056 cm2

Answer

ℓ=4 cm,A=9.6π≈3.056 cm2

Quick Solution

Question 7

MediumUnder Review

If the central angle of a sector is 60∘ and the radius of the circle is 12 cm, find the area of the sector and the percentage of the total area of the circle it represents.

Hint

Change 60∘ to radians, use A=12r2θ, then compare with πr2.

Solution

  1. Convert the angle to radians.

    The sector formula needs θ in radians, so multiply by π180.

    θ=60×π180=π3 rad
  2. Find the area of the sector.

    Use As=12r2θ.

    As=12×122×π3=144π6=24π cm2≈75.40 cm2
  3. Find the area of the circle.

    The whole circle has area πr2.

    Ac=π×122=144π cm2
  4. Find the percentage.

    Divide the sector's area by the circle's area and multiply by 100. Working with the exact values keeps π out of the answer.

    Percentage=24π144π×100%=16×100%=1623%≈16.67%

Answer

A=24π≈75.40 cm2,Percentage≈16.67%

Quick Solution

Question 8

MediumUnder Review

Find the percentage of the area of a sector subtending an angle of π8 radians.

Hint

The fraction of the circle is θ2π; the radius cancels.

Solution

  1. Write the sector area in terms of the radius.

    Let the radius be r. The sector area is 12r2θ.

    As=12r2×π8=πr216
  2. Compare with the area of the circle.

    The circle's area is πr2. The radius cancels, so the answer does not depend on the size of the circle.

    Percentage=πr2/16πr2×100%=10016%=6.25%

Answer

6.25%

Quick Solution

Question 9

HardUnder Review

A circular sector of radius r=12 cm has an angle of 150∘. This sector is cut out and then bent to form a cone. What is the slant height and radius of the base of the cone?

(Figure: a sector with centre O, both bounding radii 12 cm and central angle 150∘.)

Hint

The sector's radius becomes the slant height, and its arc length becomes the base circumference.

Solution

  1. Find the slant height.

    When the sector is rolled into a cone, its two straight edges (the radii) run from the tip of the cone to the base edge, so the sector's radius becomes the cone's slant height.

    ℓ=12 cm

  2. Find the arc length of the sector.

    Convert 150∘ to radians, then use s=rθ.

    θ=150×π180=5π6 rad s=12×5π6=10π cm
  3. Find the base radius.

    The curved arc wraps round to become the circumference of the cone's base, so 2πR=s.

    2πR=10πR=10π2π=5 cm

Answer

Slant height=12 cm,base radius=5 cm

Quick Solution

The exercises and question numbering reproduced on these pages are from Mathematics for Class 9 (National Curriculum of Pakistan 2023), published by the Punjab Curriculum and Textbook Board (PCTB), Lahore, authored by Muhammad Akhtar Shirani, Madiha Mahmood, and Ghulam Murtaza. PCTB holds the copyright in the original textbook. PrepSure is not affiliated with, endorsed by, or sponsored by PCTB. The worked solutions, explanations, hints and method notes are PrepSure's own original work, written and reviewed by our team. If you hold rights in this material and believe anything here exceeds fair use, write to us and we will take it down.

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