Basic Maths Grand Test- Q13

0 votes

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Which of the above are CORRECT ?

A. Only (A)

B. (A) and (C)

C. (B) and (C)

D. (B) and (D)

asked Nov 18, 2019 in Basic Maths by gbmentor (90,880 points)
reshown Nov 20, 2019 by getgatebook

1 Answer

+1 vote

f(x)=cos2x+cos4x

f^{'}(x)=0

(-sin2x*2)-(sin4x*4) =0

cos2x=\frac{-1}{4}

As you can see, there are 4 points in (-\Pi,\Pi) where cos2x=\frac{-1}{4}

And also f(x)=cos2x+cos4x attains its maximum value at x=0.

So option C.(B) and (C) is correct.

answered Nov 20, 2019 by (2,920 points)
edited Nov 21, 2019 by
cos2x = -1/4
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