Question

Triangle ABC is an isosceles triangle. Angles B and C are base angles, with measurements of (11x −10)° and (7x + 10)°, respectively. What is m∠A?

Group of answer choices

90°

85°

35°

5°

Answer 1

m∠A = 90°

Explanation:

In isosceles triangle base angles are congruent. That means we can equate measurments of angle B and angle C and solve for x!

m∠B = m∠C

11x - 10 = 7x + 10

4x - 10 = 10

4x = 20

x = 5

Now let's insert x back in the expressions for angles.

m∠B = (11x − 10)° = (11(5) − 10)° = 45°

m∠C = (7x + 10)° = (7(5) + 10)° = 45°

Sum of all angles in the triangle is 180°. Let's make an equation.

m∠A + m∠B + m∠C = 180°

m∠A + 45°+ 45° = 180°

m∠A = 90°