In a right-angled triangle ABC (with a right angle C), the angle A is 23 °. Find angle B.

A rectangular triangle is a triangle in which one of the corners is a straight line (equal to 90º).

Since the sum of all the angles of the triangle is 180º, the angle C is 90º, and the angle ∠A is 23º, then to calculate the angle ∠B you need to find the difference between the sum and the known angles:

∠В = 180º – ∠А – ∠С;

∠В = 180º – 23º – 90º = 67º.

Answer: the angle ∠B is equal to 67º.