Posted by eve on .
I need to find out the type of triangle (by the type of angles). Is triangle acute, right or obtuse, when the lenghts of triangle sides are:
a) 7, 8, 12
b) 20, 15, 40
c) 2/3, 8/9, 10/9

math 
Reiny,
The largest angle is opposite the largest side.
So all we have to do is check if the largest side is greater or smaller than a "hypotenuse"
in 1st:
7^2 + 8^2 = 113
12^2 = 144
so 12^2 > 7^2 + 8^2
and the triangle is obtuse with the angle opposite 12 as > 90°
2nd:
a trick question!
To form a triangle, the sum of any two sides has to be greater than the third side,
but 20+15 is NOT greater than 40.
So we can't even form the triangle.
3rd:
2/3, 8/9, 10/9
or
6/9, 8/9, 10/9
this triangle has the same angles as
6 , 8, 9 (they are similar)
check for 9^2 vs 6^2 + 8^2