I'm stuck on this homework question. I forgot the formula to find the side. This is 9th grade geometry.

Answer:
x = 2root(22)
see image.
Step-by-step explanation:
The triangle shown is one big triangle cut into two more smaller triangles: one medium-sized and one smaller.
ALL THREE TRIANGLES ARE SIMILAR BY AA.
Set the two smaller triangles up so you can see the corresponding sides. x is the short leg in one triangle and it is the long leg in the smallest triangle. Set up a proportion.
22/x = x/4
crossmultiply
x^2 = 22•4
x^2 = 88
square root both sides.
x = sqroot(88)
x = 2sqroot(22)
see image.