The value of c so that for all real x, the vectors $cx\vec i-6\vec j+3\vec k,\,x\vec i+2\vec j+2cx\vec k$ make an obtuse angle are:
Answer & explanation
Correct answer: option 3
$cx^2-12+6cx<0$ $∀x∈R$
$D<0$ & $c<0$
$36c^2+48c<0$
$⇒-\frac{4}{3}<c<0$
The value of c so that for all real x, the vectors $cx\vec i-6\vec j+3\vec k,\,x\vec i+2\vec j+2cx\vec k$ make an obtuse angle are:
Correct answer: option 3
$cx^2-12+6cx<0$ $∀x∈R$
$D<0$ & $c<0$
$36c^2+48c<0$
$⇒-\frac{4}{3}<c<0$