Ok, so
When given 3 triangle sides, to determine if the triangle is acute, right or obtuse, we have to do the following steps:
1. Square all 3 sides.
2. Sum the squares of the 2 shortest sides.
3. Compare this sum to the square of the 3rd side.
Then, we have to analyze the following conditions:
- if sum > 3rd side², the triangle is an acute triangle.
- if sum = 3rd side², the triangle is a right triangle.
- if sum < 3rd side², the triangle is an obtuse triangle.
Now, we have a triangle with these three sides: 15, 17, and 20.
First, let's find the sum of the square of the 2 shortest sides, which is
15² + 17² = 514
Now, the square of the 3rd side² is 400.
Note that 514 > 400!
Finally, these three sides form an acute triangle.