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Question: Answered & Verified by Expert
If cosx-sinx=-54, where π2<x<3π4, then cotx2 is equal to
MathematicsTrigonometric EquationsJEE Main
Options:
  • A 4-79
  • B 8
  • C -8
  • D 4+79
Solution:
2539 Upvotes Verified Answer
The correct answer is: 4+79
Given, 4cosx-sinx=-5
41-tan2x21+tan2x2-2tanx21+tan2x2=-5
4-4tan2x2-8tanx2=-5-5tan2x2
tan2x2-8tanx2+9=0
9cot2x2-8cotx2+1=0
cotx2=4±79
Since, π4<x2<3π82-1<cotx2<1
cotx2=4+79

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