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    4) A shape consists of a rectangular base with a semicircular top, as shown. Given that the perimeter of the shape is 40cm, show that its area, A cm^2, is given by the formula A=40r - 2r^2 – Pi r^2 / 2, where r cm is the radius of the semicircle.


    Individually, wouldn't the perimeter of the semi circle being pi*r + 2r and the rectangle be 2r + 2x?
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    (Original post by dont know it)
    4) A shape consists of a rectangular base with a semicircular top, as shown. Given that the perimeter of the shape is 40cm, show that its area, A cm^2, is given by the formula A=40r - 2r^2 – Pi r^2 / 2, where r cm is the radius of the semicircle.


    Individually, wouldn't the perimeter of the semi circle being pi*r + 2r and the rectangle be 2r + 2x?
    No because the two shapes are merged into one, so you do not count the length that is a 'wall' between the two objects.
 
 
 
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