If a¯ , b¯ , c¯ are unit vectors equally inclined to each other at an angle α(0<α<π) . Then the acute angle between a¯×b¯ and the plane containing b¯ and c¯ is sin−1(tanαm.|cot(αn)| ). Where m,n ∈I(integers), then the value of m2−n2

Let θ be the required angle, thensinθ=cos(900−θ)=|(a→×b→).(b→×c→)|a→×b→||b→×c→||=|[(a→×b→)×b→].c→sin2α|=|[(a→ . b→)b→−(b→ . b→)a→]c→sin2α| =|cosα b→ c→−a→ c→sin2α|=|cos2α−cosαsin2α|=|−cosα(1−cosα)sinαsinα|=|cosα2sin2α2sinα2sinα2cosα2| =|−cotαtanα2|=|cotαtanα2|∴ θ=sin−1(tanα2|cotα|)m=2.n=±1

If a¯ , b¯ , c¯ are unit vectors equally inclined to each other at an angle α(0<α<π) . Then the acute angle between a¯×b¯ and the plane containing b¯ and c¯ is sin−1(tanαm.|cot(αn)| ). Where m,n ∈I(integers), then the value of m2−n2

Let θ be the required angle, thensinθ=cos(900−θ)=|(a→×b→).(b→×c→)|a→×b→||b→×c→||=|[(a→×b→)×b→].c→sin2α|=|[(a→ . b→)b→−(b→ . b→)a→]c→sin2α| =|cosα b→ c→−a→ c→sin2α|=|cos2α−cosαsin2α|=|−cosα(1−cosα)sinαsinα|=|cosα2sin2α2sinα2sinα2cosα2| =|−cotαtanα2|=|cotαtanα2|∴ θ=sin−1(tanα2|cotα|)m=2.n=±1

AI Mentor

Check Your IQ

Free Expert Demo

Try Test

Courses

Dropper NEET Course Dropper JEE Course Class - 12 NEET Course Class - 12 JEE Course Class - 11 NEET Course Class - 11 JEE Course Class - 10 Foundation NEET Course Class - 10 Foundation JEE Course Class - 10 CBSE Course Class - 9 Foundation NEET Course Class - 9 Foundation JEE Course Class -9 CBSE Course Class - 8 CBSE Course Class - 7 CBSE Course Class - 6 CBSE Course

Offline Centres

If $\bar{a}, \bar{b}, \bar{c}$ are unit vectors equally inclined to each other at an angle $α (0 < α < π)$ . Then the acute angle between $\bar{a} \times \bar{b}$ and the plane containing $\bar{b} a n d \bar{c}$ is $\sin^{- 1} (\tan \frac{α}{m} . | \cot (\frac{α}{n}) |) .$ Where $m, n \in I (integers)$ , then the value of $m^{2} - n^{2}$

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

answer is C.

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Let $θ$ be the required angle, then
$\sin θ = \cos (90^{0} - θ) = | \frac{(\vec{a} \times \vec{b}) . (\vec{b} \times \vec{c})}{| \vec{a} \times \vec{b} | | \vec{b} \times \vec{c} |} | = | \frac{[(\vec{a} \times \vec{b}) \times \vec{b}] . \vec{c}}{\sin^{2} α} | = | \frac{[(\vec{a} . \vec{b}) \vec{b} - (\vec{b} . \vec{b}) \vec{a}] \vec{c}}{\sin^{2} α} |$
$= | \frac{\cos α \vec{b} \vec{c} - \vec{a} \vec{c}}{\sin^{2} α} | = | \frac{\cos^{2} α - \cos α}{\sin^{2} α} | = | - \frac{\cos α (1 - \cos α)}{\sin α \sin α} | = | \frac{\cos α 2 s i n^{2} \frac{α}{2}}{\sin α 2 \sin \frac{α}{2} \cos \frac{α}{2}} |$
$\begin{array}{l} = | - \cot α \tan \frac{α}{2} | = | \cot α \tan \frac{α}{2} | \\ ∴ θ = \sin^{- 1} (\tan \frac{α}{2} | \cot α |) \\ m = 2. n = \pm 1 \end{array}$