Mathematics

Problem

The value of

x

for which the angle between the vectors

\mathbf{a} = -3\hat{i} + x\hat{j} + \hat{k}

and

\mathbf{b} = x\hat{i} + 2x\hat{j} + \hat{k}

is acute and the angle between

\mathbf{b}

and

X

-axis lies between

\pi/2

and

\pi

satisfy a.

x > 0

x < 0

x > 1

only d.

x < -1

only