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Math Help - Trigonometric indentity problem

  1. #1
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    Angry Trigonometric indentity problem

    Can someone solve this for me i would be very grateful????????

    Using the identities for sin(A+B) and cos^2(theta)+sin^2(theta)=1.

    Find sine 65 degrees, given that sin 30=0.643 and sin 25=0.423?
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  2. #2
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    \sin(65) = \sin(90-25)= \dots
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  3. #3
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    Pickslides thankyou for your reply however i don't follow, i'm not very good at trig........
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  4. #4
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    \sin(65) = \sin(90-25)= \sin(90)\cos(25)-\sin(25)\cos(90)

    What's next?
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  5. #5
    Senior Member eumyang's Avatar
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    Quote Originally Posted by GAVREED2 View Post
    Find sine 65 degrees, given that sin 30=0.643 and sin 25=0.423?
    You really need to be careful with what you type. First of all, you wrote "sin 30" and "sin 25", but are they in degrees or radians? I assume that they are in degrees, but you need the degree symbol.

    Second, sin 30 is NOT 0.643. It is 0.5. A quick check on the calculator shows that you probably meant sin 40 ≈ 0.643.

    And third, you already posted this problem before (http://www.mathhelpforum.com/math-he...em-153105.html), but you neglected to give use sin 40 and sin 25. Please make sure to copy the ENTIRE problem accurately, because it is frustrating to try to work on a problem with incomplete or incorrect information.
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