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This shape consists of three semicircles - OCR - GCSE Maths - Question 21 - 2018 - Paper 1

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Question 21

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This shape consists of three semicircles. OP = OQ. The length of PQ is 4 cm. Show that the area, in cm², of the whole shape is 3πx².

Worked Solution & Example Answer:This shape consists of three semicircles - OCR - GCSE Maths - Question 21 - 2018 - Paper 1

Step 1

Show that the radius C is 2x.

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Answer

Given that OP = OQ and the length of PQ is 4 cm, we can conclude that both OP and OQ are equal to the radius of the large semicircle. Therefore, if we let the radius of each small semicircle (A and B) be x, then the radius of the large semicircle (C) will be:

C=2xC = 2x.

Step 2

Calculate the area of semicircles A and B.

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Answer

The area of each small semicircle (A and B) can be calculated using the formula for the area of a semicircle:

ext{Area of A} = ext{Area of B} = rac{1}{2} imes rac{ ext{π} imes r^2}{2} = rac{ ext{π} imes x^2}{2}.

Thus, the total area of semicircles A and B combined is:

$$ ext{Total Area (A + B)} = rac{ ext{π} imes x^2}{2} + rac{ ext{π} imes x^2}{2} = ext{π} x^2.$

Step 3

Calculate the area of semicircle C.

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Answer

The area of the large semicircle (C) can be calculated in a similar manner:

$$ ext{Area of C} = rac{1}{2} imes ext{π} imes (2x)^2 = rac{1}{2} imes ext{π} imes 4x^2 = 2 ext{π} x^2.$

Step 4

Find the total area of the whole shape.

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Answer

To find the total area of the entire shape, we sum the areas of the small semicircles A and B and the large semicircle C:

extTotalArea=extArea(A+B)+extArea(C)=extπx2+2extπx2=3extπx2. ext{Total Area} = ext{Area (A + B)} + ext{Area (C)} = ext{π} x^2 + 2 ext{π} x^2 = 3 ext{π} x^2.

Thus, we have shown that the area of the whole shape is indeed:

3extπx2.3 ext{π} x^2.

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