Question

If a + b + c = 0 and | a | = 5, | b | = 6 and | c | = 9, then find the angle between a and
b.

Answer 1

Given info : a + b + c = 0 and |a| = 5, |b| = 6 and |c| = 9

To find : the angle between a and c is...

solution : let θ be the angle between a and b.

we have , a + b + c = 0

⇒a + b = -c

⇒|a + b| = |-c|

⇒√(|a|² + |b|² + 2|a||b| cosθ) = |c| [ |-c| = |c|, doesn't change the value of a vector ]

⇒|a|² + |b|² + 2|a||b| cosθ = |c|²

here |a| = 5, |b| = 6 and |c| = 9

⇒5² + 6² + 2.5.6 cosθ = 9²

⇒60cosθ = 81 - 25 - 36 = 20

⇒cosθ = 1/3

⇒θ = cos¯¹(1/3)

Therefore the angle between a and b is cos¯¹(1/3)

Answer 2

Step-by-step explanation:

hope my answer wilk help u