Consider the cube in the first octant with sides O P ,   O Q and OR of length 1 , along the x-axis,…

Consider the cube in the first octant with sides OP, OQ and OR of length 1, along the x-axis, y-axis and z-axis, respectively, where O(0,0,0) is the origin. Let S12,12,12 be the centre of the cube and T be the vertex of the cube opposite to the origin O such that S lies on the diagonal OT. If p=SP, q=SQ, r=SR and t=ST, then the value of p×q×r×t is ______.

Solution


p=SP=12,-12,-12=12i^-j^-k^
q=SQ=-12,12,-12=12-i^+j^-k^
r=SR=-12,-12,12=12-i^-j^+k^
t=ST=12,12,12=12i^+j^+k^
p×q×r×t=14i^j^k^1-1-1-11-1×14i^j^k^-1-11111
=1162i^+2j^×-2i^+2j^=k^2=12

Asked in: JEE Advanced 2018 (Paper 2)

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