Question

Let  vector a = 3i + 2j + xk  and b = i - j + k, for some real x. Then  vector |a x b| = r is posible if -

Answer 1

Correct option  (2)

Explanation:

= \(\sqrt{2(x^2-x+19)}\)

=\(\sqrt{2(x^2-x-\frac{1}{4}+19-\frac{1}{4})}\)

\(=\sqrt{2(x-\frac{1}{2})^2+\frac{75}{4}}\)

\(=\sqrt{2(x-\frac{1}{2})^2+\frac{75}{2}}\)

\(\geq\sqrt{\frac{75}{2}}\) \((\because2(x-\frac{1}{2})^2\geq0)\) 

\(= 5\sqrt{\frac{3}{2}}\)

Hence r \(\geq5\sqrt{\frac{3}{2}}\)

Comments

WTF Bro sqrt(75/2) kaha se aaya bhai?

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please check the solution again........