For all the values of A,B,C and P,Q,R, the value of ∣∣
∣
∣∣cos(A−P)cos(A−Q)cos(A−R)cos(B−P)cos(B−Q)cos(B−R)cos(C−P)cos(C−Q)cos(C−R)∣∣
∣
∣∣ is:
A
1
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B
2
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C
0
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D
4
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Solution
The correct option is C0 We have, ∣∣
∣
∣∣cos(A−P)cos(A−Q)cos(A−R)cos(B−P)cos(B−Q)cos(B−R)cos(C−P)cos(C−Q)cos(C−R)∣∣
∣
∣∣ =∣∣
∣∣cosAcosP+sinAsinPcosAcosQ+sinAsinQcosAcosR+sinAsinRcosBcosP+sinBsinPcosBcosQ+sinBsinQcosBcosR+sinBsinRcosCcosP+sinCsinPcosCcosQ+sinCsinQcosCcosR+sinCsinR∣∣
∣∣=∣∣
∣∣cosAsinA0cosBsinB0cosCsinC0∣∣
∣∣∣∣
∣∣cosPsinP0cosQsinQ0cosRsinR0∣∣
∣∣=0