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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°