Question

The triangle has side lengths 10cm, 24cm, and 28cm, is it a right triangle? Explain please i dont understand

Answer 1

In every right triangle, if you add up the squares of the two
shorter sides, you get the square of the longest side. If you
don't then it's not a right triangle.

10² = 100
24² = 576

100 + 576 = 676

676 is the square of 26. 
It's NOT the square of 28.

So 10 - 24 - 28 is not a right triangle.

Answer 2

$28^2=10^2+24^2\\ 784=100+576\\ 784=776$

It's not.