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Math Help - Trigonometric integral question

  1. #1
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    Trigonometric integral question

    Greetings, I have come across a question that I for some reason cannot solve. The question states to find the integral of (csc(x))/(csc(x))-sin(x)) dx. I know the answer is tangent but I have no clue what trig identities were used to come across to that answer, any help would be greatly appreciated.

    Thanks in advance!
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  2. #2
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    Quote Originally Posted by Solid8Snake View Post
    Greetings, I have come across a question that I for some reason cannot solve. The question states to find the integral of (csc(x))/(csc(x))-sin(x)) dx. I know the answer is tangent but I have no clue what trig identities were used to come across to that answer, any help would be greatly appreciated.

    Thanks in advance!
    \displaystyle \frac{\sin{x}}{\sin{x}} \cdot \frac{\csc{x}}{\csc{x}-\sin{x}} =

    \displaystyle \frac{1}{1 - \sin^2{x}} =

    \displaystyle \frac{1}{\cos^2{x}} =

    \sec^2{x}<br />

    able to finish?
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  3. #3
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    thanks so much, I can't believe I couldn't solve it myself. But I had another question, I was just wondering if we always have to put the integral sign aswell as dx aslong as we are changing the way the problem looks for example by the use of trig identities. Do we always have to write the integral sign as long as we are solving?

    Thanks again.
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  4. #4
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    If you are simplifying the integrand, you don't need the integral signs and the dx as long as your equalities are correct.

    Once you have simplified it though, then you'd have to make a statement about the integrals being equal.

    So in this case, after you've found \frac{\csc{x}}{\csc{x} - \sin{x}} = \sec^2{x}

    then you would say

    \int{\frac{\csc{x}}{\csc{x} - \sin{x}}\,dx} = \int{\sec^2{x}\,dx}.
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    Quote Originally Posted by Solid8Snake View Post
    Greetings, I have come across a question that I for some reason cannot solve. The question states to find the integral of (csc(x))/(csc(x))-sin(x)) dx. I know the answer is tangent but I have no clue what trig identities were used to come across to that answer, any help would be greatly appreciated.

    Thanks in advance!
    \displaystyle\int\frac{Cosec(x)}{Cosec(x)-Sin(x)}dx

    Or...

    Express all terms using Sin(x)....

    \displaystyle\huge\frac{\frac{1}{Sin(x)}}{\frac{1}  {Sin(x)}-Sin(x)}=\frac{\frac{1}{Sin(x)}}{\frac{1}{Sin(x)}-\frac{Sin^2(x)}{Sin(x)}}

    =\displaystyle\huge\frac{\left(\frac{1}{Sin(x)}\ri  ght)}{\left(\frac{1}{Sin(x)}\right)}\ \frac{1}{1-Sin^2(x)}=\frac{1}{Cos^2(x)}=Sec^2(x)
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