Well, im not sure about the one on the left, but the one on the right is easy. Since the angles of every regular triangle always add up to 180, in the first one, the two angle we know add up to 120, which means that all you have to do there is 180 minus 120. If there are more acute angles, it is an acute triangle, if it has more obtuse angles, it is obtuse, if it has one right angle, it is a right triangle. The second problem is slightly harder, but not much since we already have the sides... we get x by itself by making this equation-
To find x, we subtract 12 from both sides first
We can add the x's together
Now we divide 84 by 3
Now we know that x equals 28, to see if this is true, we plus in 28 for x in the original equation.
This turns out to be true, so the answer is x equals 28. Since there are more acute angles in this triangle, it is acute.