Given,
a and b be two vectors such that ∣a∣=1,∣b∣=4 and a⋅b=2.
Also, given
c=(2a×b)−3b
Taking dot product with b both side we get,
⇒b⋅c=(2a×b)⋅b−3∣b∣2
⇒∣b∣∣c∣cosα=0−3∣b∣2
⇒∣c∣cosα=−12 {as ∣b∣=4}
Now, solving a⋅b=2
⇒∣a∣∣b∣cosθ=2
⇒cosθ=21⇒θ=3π
Now, solving
∣c∣2=∣(2a×b)−3b∣2
⇒∣c∣2=64×43+144=192
Now, squaring both side of ∣c∣cosα=−12 we get,
∣c∣2cos2α=144
⇒192cos2α=144
⇒192(1−sin2α)=144
⇒192sin2α=48