#### Answer

acute

#### Work Step by Step

Comparing the square of the longest side to the sum of the squares of the other two sides will tell you if a triangle is obtuse, acute, or right.
If $c^{2}$$\gt$$a^{2}$+$b^{2}$, then the triangle is obtuse
If $c^{2}$$\lt$$a^{2}$+$b^{2}$, then the triangle is acute
If $c^{2}$$=$$a^{2}$+$b^{2}$, then the triangle is right
Substitute in the greatest value in for c, which is 15.
Substitute the other two values, 11 and 12, in for a and b.
$c^{2}$$\square$$a^{2}$+$b^{2}$
$15^{2}$$\square$$11^{2}$+$12^{2}$
225$\square$121+144
225$\square$265
225$\lt$265
Since $c^{2}$$\lt$$a^{2}$+$b^{2}$, the triangle is acute