Question 78513
This is a trigonometry problem. They are asking you to solve for one
side of the triangle when two other sides are known.


The Pythagorean theorem is {{{a^2+b^2=c^2}}} where c is the hypotenuese
(the side of the triangle opposite the right angle) while a and b are
the other sides.


In this case, the hypotenuese (c) is 25 and one of the other sides (a) is 20.


so, via the Pythagorean theorem:

{{{25^2=20^2+b^2}}}

Solve for b:

{{{b^2=25^2-20^2}}}
{{{b^2=625-400}}}
{{{b^2=225}}}
{{{b=15}}}

An easier way to think about this is to recognize that this is really what we
call a "3-4-5 times 5" right triangle. In other words, one side is 3, another
is 4 and the hypotenuse is 5, all multiplied by 5. If you recognize that, you
right away that the unknown side is just 3*5 or 15.