3x=78+x-2 is the answer. Good luck on your homework!
Answer:

Step-by-step explanation:
Split up this Isosceles, Right Triangle into two congruent smaller right triangles. The reflexive side [the line that splits them apart] is 6 units, and both legs are 8 units, leaving the hypotenuses to AUTOMATICALLY be 10 units, according to the Pythagorean Theorem:

With this Pythagorean Triple, we know that our dimensions are correct. Now, to find the perimeter, just add up all the sides EXCEPT for the divider:
![\displaystyle 2[10] + 2[8] = 20 + 16 = 36](https://tex.z-dn.net/?f=%5Cdisplaystyle%202%5B10%5D%20%2B%202%5B8%5D%20%3D%2020%20%2B%2016%20%3D%2036)
I am joyous to assist you anytime.
The equation for this is a^2+b^2=c^2 so your equation would be 7^2+20^2=X
So you square the 7 and the 20 then take the square root of X and you get
X=21.19
:)