`vecA, vecB and vecC` are vectors such that `vecC= vecA + vecB and vecC bot vecA` and also C= A . Angle between `vecA and vecB` is :

Options

A. `pi//2`
B. `pi//4`
C. `3pi//4`
D. `pi`

Answer

C

Explanation

`cos theta = - ((a)/(b)) = - (1)/(sqrt(2))`

`theta= 135^(@)`
`c^(2) =a ^(2) + b^(2) + 2ab cos theta `
`a^(2) =a ^(2) + b^(2) + 2ab ((-a)/(b)) `
`a^(2) =a ^(2) + b^(2) - 2a^(2) = b^(2) -a^(2)`
`2a^(2)= b^(2) " "rArr" "b=asqrt(2)`