> The slope of the tangent is simply the derivative, the rate of change at 
> the given point. Unless I've screwed up the math somewhere, that would 
> be:
> 
> P1*3*(1 - t)^2*(-1) +
> P2*3*(2*(1 - t)*(-1)*t + (1 - t)^2) -
> P3*3*(2*t*(1 - t) - t^2) +
> P4*3*t^2
> 
> simplified:
> 
> 3*(P2 - P1 + (P1 - 2*P2 - P3)*2*t + (P2*3 + P3*3 + P4 - P1)*t^2)
> 
> (somebody want to check that?)
3*(P2 - P1 + (P1 - 2*P2 + P3)*2*t + (-P1 + P2*3 - P3*3 + P4)*t^2)

	Andrel

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