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Thread: Help me please

  1. #1
    Junior Member
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    Wink Help me please

    I have three problems I am stuck on and can't figure them out.
    The first deals with functions and the book comes up with the answer of 1 but I think i am losing my hair now trying to get that.

    f(3)+g(3)

    the next one is solving the variables by using the addition method
    3x-4y+4z=7
    x-y-2z=2
    2x-3y+6z=5

    the next is using cramer's rule

    3x=7y+1
    2x=3y-1
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  2. #2
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    Quote Originally Posted by kbryant05
    I have three problems I am stuck on and can't figure them out.
    The first deals with functions and the book comes up with the answer of 1 but I think i am losing my hair now trying to get that.

    f(3)+g(3)
    You need to specify which functions you have.

    Quote Originally Posted by kbryant05
    the next is using cramer's rule

    3x=7y+1
    2x=3y-1
    Rewrite as,
    $\displaystyle \left\{ \begin{array}{c}3x-7y=1\\2x-3y=-1 $
    Then the determinant is,
    $\displaystyle D=
    \left| \begin{array}{cc} 3&-7\\ 2&-3 \end{array}\right|
    $=$\displaystyle -9+14=5$
    With,
    $\displaystyle D_x=
    \left| \begin{array}{cc}
    1&-7\\
    -1&-3
    \end{array} \right|$=$\displaystyle -3-7=-10$.

    And,
    $\displaystyle D_y=
    \left| \begin{array}{cc}
    3&1\\
    2&-1
    \end{array} \right|$=$\displaystyle -3-2=-5$.

    Thus, you have
    $\displaystyle x=\frac{D_x}{D}=\frac{-10}{5}=-2$
    $\displaystyle y=\frac{D_y}{D}=\frac{-5}{5}=-1$
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