A triangle’s angles should all add up and equal 180 degrees. You can use this theorem to test if the triangle is a true triangle or if you are looking for an unknown angle.
Refer to this formula:
angle 1 + angle 2 + angle 3 + = 180.
A1 + B2 +C3 = 180 (simplified)
So let’s say you are looking for the angles in a triangle you are given 2 angles and one is marked as x. One angle measure is 50 degrees and the other is 90. You would pretty much use the formula above.
So,
50 + 90 + x = 180
First combine like terms
50 + 90 = 140
So, your new equation is
140 + x = 180
Subtract 140 from both sides
140-140=0 180-140= 40
Answer: x = 40.
Plug this in to your new old equation
50+90+x=180 (old)
50+90+40=180(new)
180=180.
This was the most basic of this it can get more complex with multiplying and dividing. So let me know if you need further explanation.
