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# Tangent to curve equation watch

1. Hiya I encountered a problem I couldn't really remember how to do.

Q. What is the equation of the tangent to the curve ( y= x*3 -2x*2 + 9)

where x = -1.

I know it's something to do with b*2 - 4ac = 0 but I just cant remember how to solve this.

Thanks for the help.
2. Reet differentiate it to find the gradient at that point.

The tangent will have the same gradient. Then use the curve formula to find the y co ordinate that corresponds to x= -1

Use y=mx +c (you know m and x and y) to work out c.

This is the equation. =)
3. Wow thanks, I can't believe I couldn't remember that.

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