Angles in a triangle

1 Hereisatriangle.

a) Thethreeverticesaretornoffthetriangleandarrangedona

straightline.

Whatisthesumofthethreeangles?

Howdoyouknow?

b) Nowmeasurethesizesofanglesa,bandcinthetriangle.

a= b= c=

c) Whatisthetotalofanglesa,bandc?

d) Completethesentence.

Anglesinatriangle©WhiteRoseMaths2020

a

b

c

ab

c

2 Workoutthesizesoftheunknownangles.

Givereasonsforyouranswers.

a)

x= because

b)

y= because

c)

z= because

d)

w= because

x

92°

47°

y

z

w

58°

31° 28°

25°

35°

3 Workouttheunknownangles.

a) c)

q= s=

b) d)

r= t=

Discussyourreasonswithapartner.

4 a) Twoanglesinatriangleare42°and57°.

Whatisthesizeofthethirdangle?

b) Twooftheanglesinatriangleare12°.

Whatisthesizeofthethirdangle?

c) Oneoftheanglesinatriangleis38°.Anotherangleistwicethe

sizeofthefirstangle.

Whatisthesizeofthethirdangle?

©WhiteRoseMaths2020

5 Sortthetrianglesintothetable.

0acuteangles 1acuteangle 2acuteangles 3acuteangles

Areanyofthecolumnsempty?Why?

6

DoyouagreewithRon?

Explainyouranswer.

p = 143° because angles in a triangle sum to 180°

and 180 – 37 = 143

37°

p

q

t

s

r

88.4°

72°

47.3°

19.5° 21.5°

42.1°

23.2°

101.6°

A B

C D E

35°

95°

65°

58°

58°

34°

96°61°