Shape and Space 1
3 marks · NormalWork out the value of angle y in the diagram below. Show all your working.
Given: AB = 6 cm, AC = 7 cm, BC = 5 cm, angle BAC = y°.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
y = 46.6° (correct to 1 decimal place) ° (±0.1)
Also accept: 46.6 degrees
Common mistakes: using sine rule incorrectly; incorrect labeling of sides
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Applies cosine rule to triangle correctly. (follow-through)
M1 · 1 mark · Substitutes correct values into the formula for cosine rule. (follow-through)
A1 · 1 mark · Calculates final angle y to correct degree of accuracy. (follow-through)
Worked solution
Let $y$ be the angle at A. Use cosine rule:
Here, $a = BC = 5$, $b = AC = 7$, $c = AB = 6$.