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Math Help - Need Help solving for Y

  1. #1
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    Need Help solving for Y

    Question:

    COSΘ= x/r COSΘ= -7/25

    Its in Quadrant III so X and Y are Negative

    X= -7 R= 25

    r=(x^2 + y^2)^1/2

    25=((-7)^2 + y^2)^1/2
    _______________________________________
    My Work

    25=((-7)^2 + y^2)^1/2

    25=(49 + y^2)^1/2

    25= 7+y

    18= y which is incorrect

    The math lab says this is the correct answer Y=-24 but i get something different. Can anyone help me solve this or explain where i went wrong.
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  2. #2
    MHF Contributor

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    Re: Need Help solving for Y

    Quote Originally Posted by oshae993 View Post
    Question:

    COSΘ= x/r COSΘ= -7/25

    Its in Quadrant III so X and Y are Negative

    X= -7 R= 25

    r=(x^2 + y^2)^1/2

    25=((-7)^2 + y^2)^1/2
    _______________________________________
    My Work

    25=((-7)^2 + y^2)^1/2

    25=(49 + y^2)^1/2

    25= 7+y
    This is your error "(a^2+ b^2)^{1/2}" is NOT (a^2)^{1/2}+ (b^2)^{1/2}

    Instead square both sides of 25= (49+ y^2)^{1/2} to get 625= 49+ y^2, y^2= 625- 49= 576.

    18= y which is incorrect

    The math lab says this is the correct answer Y=-24 but i get something different. Can anyone help me solve this or explain where i went wrong.
    Thanks from oshae993 and topsquark
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  3. #3
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    Re: Need Help solving for Y

    Need Help solving for Y-piccolo_a89825_701021.jpg

    Wow how did i do that. Thank you so much for clearing that up.
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