In a triangle ABC, angle B is 5 times angle A and angle C is 18° less than 4 times angle A. Find the size of the angles.
A triangle has 180º.
B = 5A
C = 4A - 18º
A + B + C = 180º
Substitute values of B and C in terms of A in the last equation to solve for A. Use that value to get B and C in the other two equations. Check by inserting the three values found into the last equation.