Question

if a^b^c^ are three vectors such that a^+2b^+c^=0and (a^)=3 (b^)=4 (c^)=7 find the angle between a^and ​

Answer 1

Answer:

Given aˉ+bˉ+cˉ=0 and ∣aˉ∣=3,∣bˉ∣=5,∣cˉ∣=7

Let angle between aˉ and bˉ be θ

aˉ+bˉ+cˉ=0

⇒aˉ+bˉ=−cˉ

⇒∣aˉ∣2+∣bˉ∣2+2aˉ⋅bˉ=∣cˉ∣2

⇒9+25+30cosθ=49

⇒cosθ=21

∴θ=3π

Hence, option D.

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