The formula for double the area of a circle
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SA=2(pi times r squared) + h(pi 2 r) or (easier way) 2 pi r squared + 2 pi r h
Pi r squared is the formula for the area of a circle. 2 pi r squared is twice that.
A = pi R^2 = 400 pi R^2 = 400 R = 20
The area of a full circle is pi x R squared where R = RADIUS The area of a semi circle is half of that, or pi x R squared/2
Algebraically, it is ; - A = pi r^(2) In words, it is ' Area equals 'pi' multiplied to the radius squared'. NB 'pi' is a constant at 3.141592..... usually shortened to '3.14'. The radius (r) is the distance from the circle centre to the circumference/edge. 'radius squared' is r^(2) , that is 'r' multiplied to 'r' ; r X r = r^(2) . NNB The circumference of a circle is ; C = 2 pi r Note the power/exponent of '2' becomes a coefficient. In words ' Circumference equals two multiplied to 'pi' multiplied to the radius. (NOT radius squared).