Gujarat BoardEnglish MediumSTD 12 ScienceMathsThe plane3 Marks
Question
Find the angle between the plane: 2x - y + z = 4 and x + y + 2z = 3
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Answer
We know that the angle between the planes, $\text{a}_1\text{x}+\text{b}_1\text{y}+\text{c}_1\text{z}+\text{d}_1=0$ and $\text{a}_2\text{x}+\text{b}_2\text{y}+\text{c}_2\text{z}+\text{d}_2=0$ is given by $\cos\theta=\frac{\text{a}_1\text{a}_2+\text{b}_1\text{b}_2+\text{c}_1\text{c}_2}{\sqrt{\text{a}_1^2+\text{b}_1^2+\text{c}_1^2}\sqrt{\text{a}_2^2+\text{b}_2^2+\text{c}^2_2}}$ So, the angle between 2x - y + z = 4 and x + y + 2z = 3 is given by $\cos\theta=\frac{(2)(1)+(-1)(1)+(1)(2)}{\sqrt{2^2+(-1)^2+1^2}\sqrt{1^2+1^2+1^2}}$ $=\frac{2-1+2}{\sqrt{4+1+1}\sqrt{1+1+4}}=\frac{3}{\sqrt{6}\sqrt{6}}$ $=\frac{3}{6}=\frac{1}{2}$ $\theta=\cos^{-1}\Big(\frac{1}{2}\Big)=\frac{\pi}{3}$
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