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Question

32.

32. The minimum value of the expression 3 sec2x - 4 sec x+1 is (A) -13 (B) 13 (C) 23 (D) 0

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Solution

Dear Student,
let,fx=3sec2x-4secx+1 ---1differentiating both sides w.r.t x;f'x=6secx.secx.tanx-4sec.tanxf'x=2tanx3sec2x-2secxput, f'x=02tanx3sec2x-2secx=03sec2x-2secx=0secx3secx-2=0secx0 Does not come in its range3secx-2=0 secx23 does not come in the range of secxand, tanx=0 x=0now, substitute the value of x=0, in 1 to get minimum value of the expression;So,f0=3sec20-4sec0+1=3-4+1=4-4=0

Regards.

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