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    (Original post by Danny.L)
    but now I am confused again.
    to get m = -3 I had to put the x=-1 value into it
    1 * x^-3 is the raw form
    differentiated is:
    -3 * x^-4
    so differentiated is
    -3/x^4
    then we make it specific by replacing x with -1
    this gives us
    -3/-1^4
    and thus -3/1 = -3
    so surely our sepcific gradient for the tangent is -3, we dont need to times it by -1 again.
    -3 / x^4 is the gradient of any given point on the curve.
    Replace x with -1 and surely the gradient isn't
    -3x it is just, -3 ? Do you see what I mean? :/
    That part's correct. That's where I thought you were most likely to make a mistake. You made the mistake substituting the value of x into the final equation to get c.
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    (Original post by Danny.L)
    but now I am confused again.
    to get m = -3 I had to put the x=-1 value into it
    1 * x^-3 is the raw form
    differentiated is:
    -3 * x^-4
    so differentiated is
    -3/x^4
    then we make it specific by replacing x with -1
    this gives us
    -3/-1^4
    and thus -3/1 = -3
    so surely our sepcific gradient for the tangent is -3, we dont need to times it by -1 again.
    -3 / x^4 is the gradient of any given point on the curve.
    Replace x with -1 and surely the gradient isn't
    -3x it is just, -3 ? Do you see what I mean? :/
    The gradient is -3 but that is m in the equation y=mx+c
 
 
 
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Updated: January 20, 2015
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