Exercise 4 Use the pi button on a calculator and give answers to 3's. f.
1. A circle has an area of 15 cm². Find its radius.
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2. A circle has a circumference of 190 m. Find its radius.
3. Find the radius of a circle of area 22 km².
4. Find the radius of a circle of circumference 58.6 cm.
5. A circle has an area of 16 mm². Find its circumference.
6. A circle has a circumference of 2500 km. Find its area.

1. 2.19 cm

2. 30.2m

3. 2.65 cm

4. 9.33cm

5. 14.2 mm

6.497000km²

Step-by-step explanation:

Use the pi button on a calculator and give answers to 3's.f.

1. A circle has an area of 15 cm². Find its radius.

Area of a circle = πr²

15cm² = π × r²

r² = 15cm²/π

r² = 4.7746482927568605

r = √(4.7746482927568605)

r = 2.1850968612 cm

Approximately to 3 s.f ≈ 2.19 cm

2. A circle has a circumference of 190 m. Find its radius.

The circumference of a circle = 2πr

C = 190m

Hence:

190m = 2πr

r = 190m/2π

r = 30.239439187m

Approximately to 3 s.f = 30.2m

3. Find the radius of a circle of area 22 km².

Area of a circle = πr²

22km² = π × r²

r² = 22km²/π

r² = 7.002817496

r = √(7.002817496)

r = 2.6462837142 cm

Approximately to 3 s.f ≈ 2.65 cm

4. Find the radius of a circle of circumference 58.6 cm.

The circumference of a circle = 2πr

C = 58.6cm

Hence:

58.6cm = 2πr

r = 58.6cm/2π

r = 9.3264796652cm

Approximately to 3 s.f = 9.33cm

5. A circle has an area of 16 mm². Find its circumference.

Step 1

Find the radius

Area of a circle = πr²

16 mm² = π × r²

r² = 16 mm²/π

r² = 5.092958178940651

r = √(5.092958178940651)

r = 2.2567583342mm

Circumference of a circle = 2πr

Circumference = 2 × π × 2.2567583342

= 14.179630807mm

Approximately to 3 s.f ≈ 14.2 mm

6. A circle has a circumference of 2500 km. Find its area.

Step 1

Find the radius

The circumference of a circle = 2πr

C = 2500km

Hence:

2500km = 2πr

r = 2500km/2π

r = 397.88735773km

Area of a circle = πr²

Area of the circle = π ×(397.88735773km)²

Area of the circle = 497359.19716km²

Approximately to 3 s.f = 497000km²

step-by-step explanation:

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