A traingle cannot be right angled and obtuse angled at the same time. Since a right angled triangle has one right angle the other two angles are acute.
To get rid of the 8 in the denominator, you need to do the opposite of the expression. So opposite of division is multiplication. My multiplying each side by 8, you can get rid of the 8 in the denominator. Because if you divide 8 by 8 it is 1.