Show that each of the following pairs of planes are at right angles:

(i) 3x + 4y - 5z = 7 and 2x + 6y + 6z + 7 = 0


(ii) x - 2y + 4z = 10 and 18x + 17y + 4z = 49


To find angle in Cartesian form, for standard equation of planes


For θ=90°, cos90°=0



(i)On comparing with the standard equation of a plane




=0=RHS


Hence proved that the angle between planes is 90°.


(ii) On comparing with the standard equation of a plane




=0=RHS


Hence proved that angle between planes is 90°.


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