vectors

If a₁ and a₂ are 2 non-collinear unit vectors and if |a₁ + a₂| =âˆš3, then the value of(a₁ -a₂).(2a₁ +a₂) is:

a)2

b)32

c)12

d)1

Plz show with steps as i dont know how to start..

2 Answers

|a1 + a2| =âˆš3

square both sides, use a₁²=a₂²=1

and find a₁.a₂

so (a₁ -a₂).(2a₁ +a₂) = 2a₁² - a₁.a₂ - a₂²

Correct.

The answer you get is c) 12.

Thank you.

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