# help about right triangles!

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• Oct 20th 2012, 10:47 PM
berto
help about right triangles!
hello!

i have question about right triangles and perimeter:

"If the perimeter of a right triangle is 12 and it's hypotenuse is 5, what is the area of the triangle?"

formula for area: a=bh/2

perimeter = b+h+hypotenuse = 12

this is solved by substitution?

b+h+5=12
b+h=7
b=7/h

a=bh/2

a=[(7/h)h]/2

a=7/2

a=3.5
• Oct 20th 2012, 11:01 PM
MarkFL
Re: help about right triangles!
Let $a$ and $b$ be the two legs of the right triangle. Since the perimeter is 12 and the hypotenuse is 5, we know:

$a+b=7$

By the Pythagorean theorem, we also know:

$a^2+b^2=5^2$

I recommend squaring the first equation to find $ab$, since the second equation gives you the value of the sum of the squares of the legs.