Geometry

Confusing Complementary and Supplementary Angles

Students mix up the totals and treat complementary angles as adding to 180∘180^\circ or supplementary angles as adding to 90∘90^\circ.

Quick check

Why students make it

Both words sound similar and both describe two angles that add to a fixed amount. Students often remember that there is a special sum, but not which word matches which sum.

The rule done right

Complementary angles add to 90∘90^\circ. Supplementary angles add to 180∘180^\circ.

Related resources

anglescomplementarysupplementary