How do I find the missing angle in a triangle?

Question

I’m reviewing triangle angle relationships and got stuck. If one angle is 40° and another is 65°, how do I figure out the third angle?

Answer 1

You can find the missing angle by using the triangle sum theorem, which states that the sum of the angles in a triangle is 180°. Let's call the unknown angle "x" then write and solve an equation:

40+65+x=180

Next, combine like terms:

105+x=180

Next, subtract 105 from both sides of the equation and simplify:

105-105+x=180-105

x=75°

Answer 2

missing angle = 180-40-65 = 180-105 = 75 degrees

all angles of all triangles sum to 180 degrees

or to pi radians. pi=180 degrees

missing angle = 75(pi/180) = 15pi/36 = 5pi/12 radians

Answer 3

The easy thing is that every shape, when you measure and add the angles from the inside of the shape, all add to 180 degrees.

So a triangle will have 180 degrees total amount of its three angles.

180 - 65 -40 = measure of the remaining angle.

180 - 40 = 140

140 - 65 = 75

Answer 4

To find the missing angle in a triangle, remember that the interior angles always add up to 180°.

So:

180° − 40° − 65° = 75°

✅ The third angle measures 75 degrees.