A triangle has sides with lengths of 3, 9, and 8. What is the radius of the triangles inscribed circle?

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Answer 1 · 2016-03-05T23:45:12

Heron's formula states that
Area = #sqrt(s(s-a)(s-b)(s-c))#

Where s is the sum of all sides / 2 (Also known as the semiperimeter)
a,b,c are the side lengths

From here, you can just plug in all the values.
Find that s = 10
Area = #sqrt(10(7)(1)(2))#
Get #sqrt140#

Now, we use the formula that says that

Area = semiperimeter * inradius

So we have

#sqrt140 = 10 * # radius

Therefore, the radius is #sqrt140 / 10#

We can simplify the radical and cancel out to get

#sqrt35 / 5#