Use pythagorean theorem for all of them
a. 3, 4, 5
3^2+4^2?5^2
9+16?25
25=25
right
b. 5, 6, 7
5^2+6^2=7^2
25+36=49
61>49
acute
c. 64+81=144
145>144
acute
hope this helps!
Start by writing the system down, I will use
to represent 

Substitute the fact that
into the first equation to get,

Simplify into a quadratic form (
),

Now you can use Vieta's rule which states that any quadratic equation can be written in the following form,

which then must factor into

And the solutions will be
.
Clearly for small coefficients like ours
, this is very easy to figure out. To get 5 and 6 we simply say that
.
This fits the definition as
and
.
So as mentioned, solutions will equal to
but these are just x-values in the solution pairs of a form
.
To get y-values we must substitute 3 for x in the original equation and then also 2 for x in the original equation. Luckily we already know that substituting either of the two numbers yields a zero.
So the solution pairs are
and
.
Hope this helps :)
No 3/7 do not represents the same length on the number line