For p > 0 , a vector v → 2 = 2 i ^ + p + 1 j ^ is obtained by rotating the vector v → 1 = 3…

For p>0, a vector v2=2i^+p+1j^ is obtained by rotating the vector v1=3pi^+j^ by an angle θ about origin in counter clockwise direction. If tanθ=α3-243+3, then the value of α is equal to

Solution

We have,

v1=3pi^+j^

v2=2i^+p+1j^

tanθ=α3-243+3

 

v1=v2

3p2+1=4+(p+1)2

2p2-2p-4=0

p2-p-2=0

p=2, -1 (rejected)

Now,

cosθ=v1·v2v1·v2=23p+(p+1)(p+1)2+43p2+1

cosθ=43+31313=43+313

tanθ=112-24343+3=63-2243+3

tanθ=63-243+3=α3-243+3

α=6

Asked in: JEE Main 2021 (20 Jul Shift 2)

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