ΔABC is an isosceles right triangle. Use the isosceles triangle base angles theorem and the sum of the interior angles of a triangle to determine the measures of ∠ACB and ∠ABC. answers : ∠ACB = 45° and ∠ABC = 90° ∠ACB = 45° and ∠ABC = 45° ∠ACB = 90° and ∠ABC = 90° ∠ACB = 90° and ∠ABC = 45°