finding missing angles

Pairs of angles that add up to 180º are

called supplementary angles

Any two angles which add up to 180º are known as

supplementary angles. They are easiest to spot when

they’re on a straight line, but they can also be far apart.

These two

angles must be

supplementary.

81º

bº

81º

bº

They would still be

supplementary even if

they weren’t touching,

but we couldn’t be sure

without knowing what

angle b is.

Use supplementary angles to find mystery angles a and b.

Is there anything surprising about mystery angle a?

BULLET

PA

TH

MICKY

BENNY

FOOTPRINTS

18º

CRIME SCENE SKETCH

CASE GEO180

(ANGLES AS MEASURED

BUT DRAWING NOT TO

SCALE)

81º

86º

72º

bº

aº

9º

PLAN VIEW

you are here 4 17

that’s not a coincidence…

Use supplementary angles to find mystery angles a and b.

Is there anything surprising about mystery angle a?

BULLET

PA

TH

MICKY

BENNY

FOOTPRINTS

18º

CRIME SCENE SKETCH

CASE GEO180

(ANGLES AS MEASURED

BUT DRAWING NOT TO

SCALE)

81º

86º

72º

bº

aº

9º

81º

bº

These two angles are on a straight line and

supplementary, so they add up to 180º.

81º+ bº = 180º

bº = 99º

bº

aº

These two angles are on a straight line and

supplementary, so they also add up to 180º.

aº + bº = 180º

PLAN VIEW

aº is the same as the first angle,

aº + 99º = 180º

which is supplementary with bº!

aº = 81º

18 Chapter 1

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