If the plane 2x – 3y – 6z = 13 makes an angle {\sin ^{ - 1}}(\lambda ) with the x-axis, then find the value of λ.
If the plane 2x – 3y – 6z = 13 makes an angle {\sin ^{ - 1}}(\lambda ) with the x-axis, then find the value of λ.

Answer:

Direction ratios of the x-axis are 1,0,0 and direction ratios of normal to the plane are 2,−3,−6.

The angle between the line and the plane,

sinϕ=|a·na||n

\sin \phi=\frac|{\vec{a} \cdot \vec{n} \mid}{\vec{a}|| \vec{n} \mid}

sinϕ=|a1,a2+b1·b2+c1·c2a12+b12c12·a22b22+c22

\sin \phi=\frac|{a_{1}, a_{2}+b_{1} \cdot b_{2}+c_{1} \cdot c_{2} \mid}{\sqrt{a_{1}^{2}+b_{1}^{2}-c_{1}^{2} \cdot \sqrt{a_{2}^{2}-b_{2}^{2}+c_{2}^{2}}}}

Let \phi be the angle between the x-axis and the given plane.

sinϕ=|1×2+0×(3)+0×(6)|12+02+0222+(3)2+(6)2=27ϕ=sin127

\begin{array}{l}

\sin \phi=\frac{|1 \times 2+0 \times(-3)+0 \times(6)|}{\left\{\sqrt{\left.1^{2}+0^{2}+0^{2}\right\}}\left\{\sqrt{2^{2}+(-3)^{2}+(-6)^{2}}\right\}\right.}=\frac{2}{7} \\

\Rightarrow \phi=\sin ^{1}\left(\frac{2}{7}\right)

\end{array}

Hence, \lambda=\frac{2}{7}.