Draw in these two right triangles (in green)



Those green right triangles are congruent because the legs
of one are equal in length to the corresponding legs of the
other.  Also we know that the two acute angles of a right
triangle are complementary.  So at the origin those two angles
of the green triangles make up 90°, and since the angle made
by the x-axis with (0,0) as a vertex is a straight angle or 180°,
the angle inside the given triangle is 90°.  Therefore the given
triangle is a right triangle.

Also since the two hypotenuses of the green triangle are equal in 
length, the two legs of the given triangle are equal in length,
so the given triangle is also isosceles.  

Therefore the given triangle is an isosceles right triangle and
has two 45° angles and, of course, one 90° angle. 

You only need to answer that it is a right triangle, but it's
also isosceles.

Edwin