The question is a 2-two-step Pythagoras theorem. (c^2 = a^2 + b^2)
Consider as such, If I were to draw a diagonal line along the base of the cube what is the length of the diagonal line. To find out that we use the theorem. We can substitute a for 5 and b for 5 as well. So
a^2 +b^2 = c^2
5^2 + 5^2 = c^2
25 + 25 = c^2
√50 = c
Then since the line side of the cube is on a 3d angle we need to do the same process again but now using the imaginary diagonal line that we just calculated and the height (5).
