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MEANING OF DIFFERENTIATION
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If the curve slopes up steeper than (Fig. 9), will be greater than .

Fig. 9.

Fig. 10.

If the curve slopes up very gently, as in Fig. 10, will be a fraction smaller than .

For a horizontal line, or a horizontal place in a curve, , and therefore .

Fig. 11.

If a curve slopes downward, as in Fig. 11, will be a step down, and must therefore be reckoned of