SOLUTION: What is the area of an equilateral triangle that has an altitude of 9?

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Question 576246: What is the area of an equilateral triangle that has an altitude of 9?
Answer by nerdybill(7384) About Me  (Show Source):
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What is the area of an equilateral triangle that has an altitude of 9?
An equilateral triangle tells us that all three sides are equal.
Area = (1/2)bh
first, we need to find the length of the base
Let b = length of base
then from Pythagorean theorem we have
(b/2)^2 + 9^2 = b^2
b^2/4 + 81 = b^2
81 = b^2 - b^2/4
81 = b^2(1 - 1/4)
81 = b^2(3/4)
81(4/3) = b^2
81(4/3) = b^2
108 = b^2
10.39 = b
.
Area = (1/2)bh
Area = (1/2)(10.39)(9)
Area = 46.77