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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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370 Chapter 10 Differentiation

y

y

y

y

x

x

x

(i) (ii) (iii) (iv)

Figure10.13

x

Solutions

1 (a)4 (b)2 (c)5 (d)8

2 yislinearinx,thatisy =ax +b

3 (i) always negative (ii) always positive

(iii) always positive (iv) always negative

4 (a) 2x (b) −2x +2

5 4x,12,−8,4,0

6 4−2t,0

7 (a) 0.05 (b) 0.025 (c) −0.5

10.6 EXISTENCEOFDERIVATIVES

So far we have seen that the derivative, dy , of a function,y(x), may be viewed either

dx

algebraically orgeometrically.

( )

dy y(x + δx) −y(x)

dx = lim

δx→0 δx

dy

= rate of change ofy

dx

= gradient of the graph ofy

We now discuss briefly the existence of dy . For some functions the derivative does not

dx

exist at certain points and we need to be able to recognize such points. Consider the

graphs shown in Figure 10.14. Figure 10.14(a) shows a function with a discontinuity at

y

y

(a)

a

x

Figure10.14

(a) The graphhas a discontinuity atx =a. (b)The graphhas a cuspat

x=a.

(b)

a

x

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