That's a question about the Pythagorean Theorem.
We use the Pythagorean Theorem to find the value of one side in a right triangle.
This theorem says that:

- a is the hypotenuse (It's the opposite side the right angle).
- b and c are cathetus (They're the adjacent sides the right angle).
Okay, now, let's go to solve this problem! In our figure, we have two cathetus. Their values are 10 and 7 and we have to find the value of x (the hypotenuse). Let's change this information in that formula.

Therefore, the value of x is
.
I hope I've helped. :D
Enjoy your studies! \o/