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Math Help - How to solve k and this other question.

  1. #1
    Newbie dizzycarly's Avatar
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    How to solve k and this other question.

    Hey, can you guys tell me how to figure out this.

    The graph of y=4x+k has a intercept of -20. Determine the value of k.

    and.. how do you solve..

    The line segiment joining R(k,6) and S(-4,k) has a midpoint at (-11,-6). Determine the value of k.

    thanks!
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  2. #2
    Super Member
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    Quote Originally Posted by dizzycarly View Post
    Hey, can you guys tell me how to figure out this.

    The graph of y=4x+k has a intercept of -20. Determine the value of k.
    Which intercept? An x-intercept or a y-intercept?

    If -20 is the y-intercept, then that's k. Slope-intercept form of the equation of the line is y = mx + b, and b is the y-intercept. So the equation is just
    y = 4x - 20.

    But if -20 is the x-intercept, then you plug in -20 for x and 0 for y:
    \begin{aligned}<br />
0 &= 4(-20) + k \\<br />
0 &= -80 + k \\<br />
80 &= k<br />
\end{aligned}

    So the equation would be
    y = 4x + 80.


    01
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  3. #3
    Newbie dizzycarly's Avatar
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    thanks very much I forgot to say x.

    does anyone know how to solve the second question?
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by dizzycarly View Post
    thanks very much I forgot to say x.

    does anyone know how to solve the second question?
    I like your avatar.

    for the second problem, we have by the midpoint formula:

    (-11,-6) = \left( \frac {k - 4}2, \frac {6 + k}2 \right)

    now do you see how to solve for k?
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  5. #5
    No one in Particular VonNemo19's Avatar
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    Quote Originally Posted by dizzycarly View Post
    thanks very much I forgot to say x.

    does anyone know how to solve the second question?

    If the point given in the problem is in fact the midpoint, it must satisfy these conditions

    (-11,-6) = \left( \frac {x_1+x_2}2, \frac {y_1+y_2}2 \right)


    therefore, let x_1=k and x_2=-4

    Then

    \frac{k+(-4)}{2}=-11

    Solve for k.

    You can verify the y ordinate.
    Last edited by VonNemo19; June 21st 2009 at 07:49 PM.
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