What is the perimeter of a triangle if the lengths of the sides are 8", 10", and x?

So basically you're trying to find the third side. I'd like you to meet this new equation called the Pythagorean theorem. The equation is basically a²+b²=c².

So here is where you use the formula:

Replace x and y with 8 and 10

8²+10²=c²

Now simplify the equation

8² = 64
10² = 100
64+100=c²
164=c²

now you have to remove that ² from c. So basically you cancel it by square rooting it. But if you square root one side, you have to square root the other side.

√164 = √c²
√ and ² cancel each other out...
c = √164
√164 = 12.8
c= 12.8

Wait! we're not done yet cause now you have to find the perimeter of the triangle.

12.8+8+10
=30.8
Hope this helps!