Question

What type of triangle has side lengths 9, 10, and √130? A. obtuse B. not a triangle C. acute D. right

Answer 1

Answer: Option C.

Step-by-step explanation:

The lengths of our triangle are:

9, 10 and √130.

If the triangle is a triangle rectangle, by the Pitagoream's theorem we have:

A^2 + B^2 = H^2

in this case H is the larger side, this must be √130.

then:

A and B must be 9 and 10.

9^2 + 10^2 = (√130)^2

81 + 100 = 130

This is false, so this is NOT a triangle rectangle, the hypotenuse is shorter than it should be.

Now, we have some kind of rule:

 if A^2 + B^2 = H^2 then we have one angle of 90° and two smaller ones. (triangle rectangle)

 if A^2 + B^2 > H^2 then all the angles are smaller than 90°, this is an acute triangle.

 if A^2 + B^2 < H^2 then we have one angle larger than 90°, this is an obtuse angle.

(H is always the larger side, A and B are the two shorter ones).

In this case:

81 + 100 > 130

Then this must be an acute angle.