Determining Complementary and Supplementary Angles
In Fig. 8.10, we see that m∡ABC = 31°.
a) ∡ABC and ∡CBD are complementary angles. Determine m∡CBD.
b) ∡ABC and ∡CBE are supplementary angles. Determine m∡CBE.
a) The sum of two complementary angles must be 90°, so
m∡ABC + m∡CBD = 90°
31° + m∡CBD = 90°
m∡CBD = 90° – 31° = 59° Subtract 31° from each side of the equation.
b) The sum of two supplementary angles must be 180°, so
m∡ABC + m∡CBE = 180°
31° + m∡CBE = 180°
m∡CBE = 180° – 31° = 149° Subtract 31° from each side of the equation.