Answer:
5.7
Step-by-step explanation:
The altitude of a right triangle divides it into two smaller triangles, all three of which are similar.
ΔABC ~ ΔADB ~ ΔBDC
Writing and solving a proportion:
AD / BD = BD / CD
(x + 3) / 5 = 5 / (2x + 3)
(x + 3) (2x + 3) = 25
2x² + 9x + 9 = 25
2x² + 9x − 16 = 0
x = [ -9 ± √(81 − 4(2)(-16)) ] / 2(2)
x = [ -9 ± √(81 + 128) ] / 4
x = (-9 ± √209) / 4
x = -5.86 or 1.36
Since x can't be -5.86, x = 1.36. So the length of CD is:
CD = 2(1.36) + 3
CD = 5.7
