The pythagorean theorem describes the relationship between the lengths of legs a and b and the hypotenuse c of any right triangle. a 2 + b 2 = c 2 complete the equation below by writing an expression equivalent to the length of a, the leg of a right triangle.

Sorry. I should have known.
a = square root of (c^2 - b^2)
Does your marker let you omit the ^ meaning power of?
Be careful about how you enter that.
I don't think it would be correct to write square root of (c 2 - b 2) but maybe you can do that if you and your marker have agreed on it.