Expressions, equations & relationships · TEKS 7.11C
Angle relationships
Angle pairs have fixed sums. Write an equation from the sum, then solve.
Key steps
- Complementary: add to 90°.
- Supplementary (straight line): add to 180°.
- Vertical angles (an X shape): equal.
- Triangle: all three angles add to 180°.
Worked example
Angles x°, 2x° and (x + 20)° form a triangle. Find x.
- x + 2x + x + 20 = 180.
- 4x = 160, so x = 40.
- Answer: x = 40
Watch out: Read what is asked: x, or the size of an angle? After finding x, plug it back in if needed.
Practice
5 questions with new numbers every set. Get 4 of 5 to mark this topic as practiced.