Question

7.
Find the angle between Ā & B, B & C, C &Ā.
500
70°C
600​

Answer 1

Explanation:

Given, a+b+c=0

and ∣a∣=5,∣b∣=3,∣c∣=7

⇒a+b=c

On squaring both sides, we get

(a+b)2=(−c)2

⇒∣a+b∣2=∣c∣2

⇒∣a∣2+∣b∣2+2a⋅b=∣c∣2

(∵θ be the angle between a and b)

⇒(5)2+(3)2+2∣a∣∣b∣cosθ=(7)2

⇒25+9+2⋅5⋅3cosθ=49

⇒30cosθ=15

⇒cosθ=21=cos60∘

⇒θ=3π