Question 256162
Is a triangle a right, acute, or an obtuse triangle if 
has the measures 11, 11, and 15?
<pre>
The only angle that could be obtuse or right in any triangle
is the angle opposite the longest side.

Let a = 15, b= 11, c = 11, then A is the angle opposite the 
longest side 15 

{{{cos(A) = (b^2+c^2-a^2)/(2bc)}}}
{{{cos(A) = (11^2+11^2-15^2)/(2(11)(11))}}}
{{{cos(A) = .0702479339}}}
{{{A="85.97177216°"}}}

That's less than 90°, so it's acute!  Thus the triangle
is an acute triangle.

Edwin</pre>