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Which of the following statements is/are TRUE ?

A. The sine of the angle between the vectors a⃗=i^+3j^−2k^\vec{a}=\hat{i}+3\hat{j}-2\hat{k} and b⃗=−2i^+2j^−4k^\vec{b}=-2\hat{i}+2\hat{j}-4\hat{k} is 27\frac{2}{\sqrt{7}}

B. The area of the parallelogram PQRS is 12∣PR⃗×QS⃗∣\frac{1}{2}|\vec{PR}\times\vec{QS}|

C. If a⃗=5i^−4j^+3k^\vec{a}=5\hat{i}-4\hat{j}+3\hat{k} then ∣a⃗×i^∣2+∣a⃗×j^∣2+∣a⃗×k^∣2=100|\vec{a}\times\hat{i}|^2+|\vec{a}\times\hat{j}|^2+|\vec{a}\times\hat{k}|^2=100

D. Vectors perpendicular to the vectors a⃗=2i^−j^+2k^\vec{a}=2\hat{i}-\hat{j}+2\hat{k} and b⃗=−i^+4j^−3k^\vec{b}=-\hat{i}+4\hat{j}-3\hat{k} are given by λ(−i^+2j^+2k^)\lambda(-\hat{i}+2\hat{j}+2\hat{k}) where λ\lambda is a scalar.

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 4

A: a⃗⋅b⃗=12\vec a\cdot\vec b=12, ∣a⃗∣=14|\vec a|=\sqrt{14}, ∣b⃗∣=26|\vec b|=2\sqrt6, so cos⁡2θ=37\cos^2\theta=\frac37 and sin⁡θ=27\sin\theta=\frac{2}{\sqrt7}, true. B: the diagonals formula for a parallelogram's area is a standard identity, true. C: the sum equals 2∣a⃗∣2=2(50)=1002|\vec a|^2=2(50)=100, true. D: a⃗×b⃗=−5i^+4j^+7k^\vec a\times\vec b=-5\hat i+4\hat j+7\hat k, not proportional to −i^+2j^+2k^-\hat i+2\hat j+2\hat k, so false.

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