What you’ll learn
Solve complementary-angle problems.
Key idea
Complementary angles have the specified sum; an algebraic label represents the whole unknown angle measure.
Complementary angles sum to90; the algebra parameter differs from the entire angle measure.
Worked example
Enter the exact value or ordered values in the format requested below.
Angles A and B are complementary. A=78°, and B is labeled (2x+8)°. Find B's measure in degrees as a number, not x.
- Complementary angles have sum 90°; the missing measure is 90-78=12°.
- Its label 2x+8 gives 2x+8=12, so x=(12-8)/2=2.
Answer: 12
Quick Check
Evaluate a worked attempt at solve complementary-angle problems, identify the first invalid step, and provide the correction.
A=77°, B=(2x+1)° are complementary. Step1 identifies that relationship. Step2 sets A+B=180° and B=103°. Locate the first invalid step and correct B.