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Write $x_2=x_1+h$ and let $h$ approach zero through nonzero values. The nearby secants illustrate the search for one limiting slope at the fixed base point.

Conditions: $x_2$ is expressed as $x_1+h$.; $h$ approaches zero through nonzero values.

Write $x_2=x_1+h$ and let $h$ approach zero through nonzero values. The nearby secants illustrate the search for one limiting slope at the fixed base point.

Conditions: $x_2$ is expressed as $x_1+h$.; $h$ approaches zero through nonzero values.