Could you please help me with this question?

  • Thread starter phy_
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  • #1
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-10.5 = 3.8 cos [2pi/360(x-172)] this is the question and i am trying to solve for x though i don't know that i can break away the x from cos the way i did... is there another way??
i don't think the answer should be negative as the question is looking for a day of the year.

so if i try to solve for x, i end up with

-2.76 = cos [0.017x - 2.924]

-1.8876 = cos 0.017x

-1.8876/0.9999 = x

x = -1.8878
 

Answers and Replies

  • #2
Mentallic
Homework Helper
3,798
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There is no solution to the equation.

Reason is that the cosine of a value ranges between -1 and 1.

[tex]A=Bcos\theta[/tex]

[tex]cos\theta=\frac{A}{B}[/tex]

Therefore, to have a real solution for [itex]\theta[/itex], [tex]-1\leq \frac{A}{B}\leq 1[/tex]

But in the case of your equation:

[tex]-10.5=3.8cos(\frac{2\pi (x-172)}{360})[/tex]

[tex]cos(\frac{2\pi (x-172)}{360})=\frac{-10.5}{3.8}[/tex]
 

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