Problem:
Let be the center of the incircle of triangle . Suppose that this incircle has radius , and that . If the area of the triangle is , what is the length of ?
(a) 670
(b) 672
(c) 1340
(d) 1344
Problem:
Let be the center of the incircle of triangle . Suppose that this incircle has radius , and that . If the area of the triangle is , what is the length of ?
(a) 670
(b) 672
(c) 1340
(d) 1344
Solution:
Let be the inradius, . Let be the area, . Let .
Recall that , where is the semiperimeter. So:
Let be the distance from to the incenter . There is a formula:
But this is complicated. Alternatively, recall that:
So:
Given , , :
So or
But must be less than (since is a side, is the semiperimeter), and must be positive. Both and are possible, but let's check which is correct.
If , then , which is not possible (since is the sum of the other two sides divided by and must be positive). So .
Thus, the answer is .