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If θ is the angle between the planes a1x + b1y + c1z + d1 = 0 and a2x + b2y + c21z + d2 = 0 then(a) .(b) True(c) FalseThe question was posed to me during an internship interview.Asked question is from Three Dimensional Geometry in chapter Three Dimensional Geometry of Mathematics – Class 12

Answer»

Correct choice is (B) True

Explanation: The formula to find angle between the NORMAL of two PLANES is

cos θ=\(\FRAC {a1a2+b1b2+c1c2}{\sqrt {a1^2+b1^2+c1^2} \sqrt{a2^2+b2^2+c2^2 }}\) not cos θ=\(\frac {a1a2.b1b2.c1c2}{\sqrt {a1^2+b1^2+c1^2} \sqrt {a2^2+b2^2+c2^2 }}\) because the numerator should contain SUM of co-efficients not their product.



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