Practicing Success
If unit vector $\vec c$ makes an angle $\frac{\pi}{3}$ with $\hat i+\hat j$, then minimum and maximum values of $(\hat i×\hat j).\vec c$ respectively are: |
$0,\frac{\sqrt{3}}{2}$ $-\frac{\sqrt{3}}{2},\frac{\sqrt{3}}{2}$ $-1,\frac{\sqrt{3}}{2}$ None of these |
$-\frac{\sqrt{3}}{2},\frac{\sqrt{3}}{2}$ |
$\vec c=x\hat i+y\hat j+x\hat k$ $x+y=\sqrt{2}\frac{1}{2}$ $x+y=\frac{1}{\sqrt{2}},y=\frac{1}{\sqrt{2}}-x$ $x^2+y^2+z^2=1,y^2=\frac{1}{2}+x^2-\sqrt{2}x$ $∴z^2=1-x^2-\frac{1}{2}-x^2+\sqrt{2}x=\frac{1}{2}-2x^2+\sqrt{2}x$ $\hat k.\vec c=z$ $x^2+y^2+2xy=\frac{1}{2}$ $z^2_{man}≤\frac{3}{4}=z∈[-\frac{\sqrt{3}}{2},\frac{\sqrt{3}}{2}]$ |