Question

A triangle can have at most ________ right angle.

Answer 1

A triangle can only have at most one right angle.

Here's a proof that shows why this is so:

We know that the sum of all interior angles of a triangle must add up to 180.
Let's say the interior angles are A, B, and C

A + B + C = 180

Let's show that having two right angles is impossible

Let A = B = 90

90 + 90 + C = 180

180 + C = 180

Subtract 180 from both sides

C = 0

We cannot have an angle with 0 degrees in a triangle. Thus, it is impossible to have 2 right angles in a triangle.

Let's try to show that it's impossible to have 3 right angles

Let A = B = C = 90

90 + 90 + 90 = 180 ?

270 ≠ 180

Thus it's impossible to have 3 right angles as well.

Let's show that is possible to have 1 right angle

Let A = 90

90 + B + C = 180

Subtract both sides by 90

B + C = 90

There are values of B and C that will make this true. Thus, a triangle can have at most one right angle.

Have an awesome day! :)