March 2009, Vol. 102, Issue 7
Tangent Lines without Derivatives for Quadratic and Cubic Equations
William Carroll
In the quadratic equation, y = ax<sup>2</sup> + bx + c, the equation y = bx + c is identified as the equation of the line tangent to the parabola at its y–intercept. This is extended to give a convenient method of graphing tangent lines at any point on the graph of a quadratic or a cubic equation.
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