JEE MAIN - Mathematics (2023 - 13th April Morning Shift - No. 21)
Explanation
Given that $$\vec{a} = \vec{b} \times \vec{c}$$, we can find the magnitudes of $$\vec{a}$$ and $$\vec{c}$$:
$$|\vec{a}| = \sqrt{3^2 + 1^2 + (-1)^2} = \sqrt{11}$$
$$|\vec{c}| = \sqrt{2^2 + (-3)^2 + 3^2} = \sqrt{22}$$
We know that the magnitude of the cross product of two vectors is equal to the product of the magnitudes of the vectors and the sine of the angle between them :
$$|\vec{a}| = |\vec{b} \times \vec{c}| = |\vec{b}||\vec{c}|\sin\theta$$
Plugging in the known values :
$$\sqrt{11} = \sqrt{50}\sqrt{22}\sin\theta$$
Solving for the sine of the angle between the vectors :
$$\sin\theta = \frac{1}{10}$$
Now we can find $$|\vec{b} + \vec{c}|^2$$ using the formula :
$$|\vec{b} + \vec{c}|^2 = |\vec{b}|^2 + |\vec{c}|^2 + 2\vec{b} \cdot \vec{c}$$
We have the dot product $$\vec{b} \cdot \vec{c} = |\vec{b}||\vec{c}|\cos\theta$$, and we can use the relationship between sine and cosine: $$\cos\theta = \sqrt{1 - \sin^2\theta} = \frac{\sqrt{99}}{10}$$.
Substitute the values into the formula :
$$|\vec{b} + \vec{c}|^2 = 50 + 22 + 2\sqrt{50}\sqrt{22}\frac{\sqrt{99}}{10} = 72 + 66$$
Finally, we need to find the absolute value of the difference :
$$|72 - |\vec{b} + \vec{c}|^2| = |72 - (72 + 66)| = 66$$
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