Q&A for How to Find the Third Angle of a Triangle

Take the 90, add it to 35. This gives you 125 degrees. Triangles can only ever add up to 180, thus take the difference of 125 and 180 (180-125). This will give you the third remaining angle, which in this case is 55.

A right angle triangle always consists of one 90 degree angle, and every triangle must equal 180 degrees. Here is the work for this problem: 90 degrees (representing the right angle) + 50 degrees equals 140 degrees. 180 minus 140 equals 40. Therefore, the remaining angle would be 40 degrees.

Substitute a letter, and work it out like an algebraic equation that you have to solve.

Add the two angles you already know (for example, 50 and 45), then, with the sum of the two angles (95), subtract it from 180 (180-95) and there's your answer.

The three angles of any triangle add up to 180 degrees. Since you know two angles (35 and 40), add them together, then subtract the total from 180 to determine the degree of the third angle.

If you know the lengths of the sides, you can use trigonometry. Otherwise, you can't do it with the information given.

That ratio is actually 2:1:4. Add those three numbers to get 7. Divide 7 into 21,000. Multiply the quotient by 2, 1, and 4 separately to get the three numbers you're looking for.

Add 1 + 4 + 7. That's 12. Divide 12 into 180, the total number of degrees in a triangle's three angles. 180 ÷ 12 = 15. Multiply 15 by 1, 4, and 7 respectively to get 15, 60, and 105. Those are the number of degrees in the three angles you want. Use a protractor and a straightedge to construct the triangle.

It's not possible to do that.

A right triangle always contains one 90° angle. One of the other angles is given as 55°. Add 90° and 55°, then subtract that sum from 180°. That gives you the third angle.

The interior angles of a polygon add up to (n-2)(180°), where n is the number of sides. In the case of a pentagon, the angles add up to 3 x 180° = 540°. If you know four of the angles, add them together, and subtract the sum from 540°.

The exterior angle of a 45° angle is 135°. You can't determine the other exterior angles if you don't know the other interior angles.

Use a protractor to accurately measure angles in a triangle.

A triangle is defined as containing three angles that add up to 180°.

x is a negative 12.

Because AB = AC, angles B and C are equal to each other and to x. Then angle A = 180° - 2x.

To do this, you must set a system of equations. X= the first angle and Y= the second angle. Now set it up as follows (suggested): X - Y = 30, X + Y = 110. Now, using the addition method, you can eliminate Y so now it will look like this: 2X = 140. Divide by 2: X = 70. Therefore 70 is one of the angles. To get the other, plug it back into the system into one of the equations: 70 + Y = 110 and now solve: Y = 40. Check your answers: 70(X) - 40(Y) = 30(Small angle), 70(X) + 40(Y) = 110(Large angle). Now take the sum and subtract that from 180: 180-110=70.