What is the area of a circle with a diameter of 4, 9, and 11 ft?

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Answer 1 · 2018-03-29T00:45:44

The areas in #ft^2# are:

# d = 4 => A = 4pi#

# d = 9 => A = 81/4pi#

# d = 11 => A = 121/4pi#

The area of a circle of radius #r# is given by the well known formula:

# A = pir^2 #

If the diameter is #d# the we have #d=2r => r=d/2#, thus we have:

# A = pi(d/2)^2 = (pid^2)/4#

Thus, we have:

# d = 4 => A = (pi4^2)/4 =4pi#

# d = 9 => A = (pi9^2)/4 =81/4pi#

# d = 11 => A = (pi11^2)/4 =121/4pi#