Radius of a sector of a circle?

Question

What is the radius of a sector of a circle with a central angle of measure 90° and whose area is 4π cm2?

1) 8cm

2) 4cm

3) 12cm

4) 3/4 cm

What is the radius of a sector of a circle with a central angle of measure 45° and whose area is 9/8πcm^2

1) 8cm

2) 4/3cm

3) 9/4cm

4) 3cm

Answer 1

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1:

area of a sector=90/360xπ(r^2)

4π=0.25π(r^2)

cut out π

4/0.25=r^2

taking square root on both sides:

r=4

so the answer is 4cm.

2:

area of a sector=90/360xπ(r^2)

9/8πcm^2=45/360π(r^2)

following the same procedure as done above

the answer is 3cm

Answer 2

First one => Entire area = 4π * 4 = 16π cm^2 => r = 4 cm