Question

how do you find the missing lenght of a right triangle if you have 20 on the left side and 48 on the bottom and you need to find the missings number

Answer 1

Pythagoras theorem tells us that for a right-triangle,
a² + b² = c²
where a and b are sides adjacent to the right-angle, and c is the hypothenuse.

It is not clear from the question whether the sides of lengths 20 and 48 are adjacent to the right-angle.

If that's the case, the hypothenuse is
√(20²+48²)
=√(1696)
=41.2 approximately.

Answer 2

is this a right angle triangle?
if it is you can find the hypotenuse which is the longest side of the triangle using Pythagoras theorem
a(squared)+b(squared)=c(squared)
c=hypotenuse
20(squared)+48(squared)=c(squared)
400+2304=c(squared)
2704=c(squared)
(square root)2704=c
52=c