- #1

- 113

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f(x) = 3cos(4*pi*x-1.3) + 5cos(2*pi*x+0.5).

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- Thread starter AlbertEinstein
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- #1

- 113

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f(x) = 3cos(4*pi*x-1.3) + 5cos(2*pi*x+0.5).

- #2

HallsofIvy

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Looks pretty straight forward to me: differentiate and set the derivative equal to 0. Use the sin(a+b) formula to isolate [itex]sin(3\pi x)[/itex] and [itex]cos(3\pi x)[/itex].

- #3

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Hey HallsofIvy,

Your suggestion was quite correct. However I dare say differentiating and equating to zero does not always help.

Here f (x) = 3cos (4*pi*x-1.3) + 5cos (2*pi*x+0.5)

Or, f’ (x) = - [12*pi*sin (4*pi*x-1.3) + 10*pi*sin (2*pi*x+0.5)]

Equating this to zero,

12*pi*sin (4*pi*x-1.3) + 10*pi*sin (2*pi*x+0.5)] = 0

Now if I use the sin (a+b) formula the equation gets rather complicated.

I shall be thankful to you if you could please show the full solution.

However the answer is 5.7811.

- #4

HallsofIvy

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