Practicing Success
The values of x for which the angle between the vectors $2x^2\hat i+4x\hat j+\hat k$ and $7\hat i-2\hat j+x\hat k$ is obtuse and the angle between the Z-axis and $7\hat i-2\hat j+x\hat k$ is acute and less than $\frac{\pi}{6}$ is given by: |
$0<x<\frac{1}{2}$ $x>\frac{1}{2}$ or x < 0 $\frac{1}{2}<x<15$ No such value for x |
No such value for x |
$14x^2-8x+x<0$ $14x^2-7x<0$ $7x(2x-1)<0$ $⇒x∈(0,\frac{1}{2})$ $7\hat i-2\hat j+x\hat k$ $\hat k∈(0,\frac{\pi}{6});cosθ∈(\frac{\sqrt{3}}{2},1)$ $\frac{\sqrt{3}}{2}<\frac{x}{\sqrt{53+x^2}}<1⇒\frac{3}{4}<\frac{x^2}{53+x^2}<1⇒4x^2>159+3x^2⇒x^2>159$ |