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# Ugh. Differentiation help. watch

1. (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.
2. (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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