A triangle with sides of lengths 10, 18 and 21 is a right triangle?

it's false

Step-by-step explanation:

i just took the test

No. Se below for explanation

Step-by-step explanation:

If it is a right triangle it sides must meet the Pitgoras Theorem, wich says that the legs squared when summed must be equal to the square of the hypotenuse. Here the legs would be the sides of length 10 and 18, as the hypotenuse is always the longest. So we need to see:

10^ 2 + 18^2 = x

if x is equal to 21^2, so we can have a right triangle, if not, we cannot.

10^ 2 + 18^2 = 100 + 324

10^ 2 + 18^2 = 424

But:

21^2 = 441

So, as 10^2 + 18^2 < 21^2 this can not be a right triangle.