Question

what is x for number 14.

Answer 1

x^2$(x+7)^2=x^2+10^2 x^2+14x+49=x^2+100 14x+49=100 14x=51 x=3.64$

Answer 2

It's a right triangle.  So

         (x²) + (10²)  =  (7+x)²

         x²  +  100  =  49 + x² + 14x

That may look ugly, but I'm pretty sure you can handle it from this point.

Wow !  I just noticed that you can subtract  x²  from each side
and not even have to mess with it again.