Question 238515
For every triangle,
{{{A+B+C=180}}}
where A,B,C are the angles.
An obtuse angle is an angle greater than 90 degrees. 
Let A be an obtuse angle. 
Then A=90+e, where e is a positive value, less than 90. 
{{{90+e+B+C=180}}}
{{{e+B+C=90}}}
B and C cannot equal 0. 
{{{0<e<90}}}
Then
{{{B+C<90}}}
{{{0<B<90}}}
{{{0<C<90}}}
which means they are both acute.