Geometry · Angles · 1.3

Supplementary angles.

Two angles are supplementary when they add up to 180° — together they make a straight line. Subtract the known angle from 180°. The supplement of 110° is 70°.

01 / THE IDEA

See it work.

The figure

See the shape.

110°

Watch the method

Supplementary angles

Supplement of a° = 180 − a.

1 / 2
1

Supplementary angles

Two angles are supplementary when they add to 180° (a straight line).

?+110∘=180∘? + 110^\circ = 180^\circ
2

Subtract

Subtract the known angle from 180°.

180−110=70∘180 - 110 = 70^\circ
02 / YOUR TURN

Practice until it feels automatic.

Your turn

Find the measure.

Type the number — units optional.

streak 0
best 0

…

— / WHY IT WORKS

The idea underneath.

Make a straight line

Supplementary angles sit on a straight line, so they total 180°.

Why it works

Two angles on a flat line.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Find the supplement of 66°.

1

Supplementary angles

Two angles are supplementary when they add to 180° (a straight line). ? + 66° = 180°

2

Subtract

Subtract the known angle from 180°. 180 - 66 = 114°

EX 2medium

Find the supplement of 83°.

1

Supplementary angles

Two angles are supplementary when they add to 180° (a straight line). ? + 83° = 180°

2

Subtract

Subtract the known angle from 180°. 180 - 83 = 97°

EX 3hard

Find the supplement of 94°.

1

Supplementary angles

Two angles are supplementary when they add to 180° (a straight line). ? + 94° = 180°

2

Subtract

Subtract the known angle from 180°. 180 - 94 = 86°

04 / COMMON TRAPS

Where students slip.

Trap

Using 90° instead of 180°.

Fix

Supplementary is 180°.

Trap

Sign slips.

Fix

Subtract the known angle from 180°.

05 / QUIZ

Test yourself.

The Test

12 problems across three tiers. Auto-graded on submit. Hints and a full walkthrough on every question. Your work is saved on this device — sign in to keep it across devices.

0/12Answered
How to answerType just the value. Formatting won't trip you up — we ignore spaces, capital letters, commas, and subscript style, so t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).
Core

Core (4)

C1

Find the supplement of 160°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
C2

Find the supplement of 107°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
C3

Find the supplement of 119°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
C4

Find the supplement of 35°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
Apply

Apply (4)

A1

Find the supplement of 66°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
A2

Find the supplement of 154°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
A3

Find the supplement of 93°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
A4

Find the supplement of 113°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
Extension

Extension (4)

E1

Find the supplement of 76°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
E2

Find the supplement of 87°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
E3

Find the supplement of 96°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.
E4

Find the supplement of 145°.

Need a hint?
  • Supplementary angles add to 180°.
  • Subtract from 180°.