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To show the right angle between two planes, we simply find the angle between the normal vectors of planes. So if n1 and n2 are normal vectors and θ is the angle between both then

.for right angle θ=90°

Cos90°=0

(1)

(i)On comparing with standard equation

Hence proved planes at right angles.

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

Hence proved planes at right angles.