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dy<br />

dx = lim<br />

D ®<br />

f(u + Du) − f(u)<br />

. lim<br />

Du D ®<br />

Persamaan 5.12 disebut aturan rantai<br />

Du<br />

Dx = dy du<br />

dx dx (terbukti)<br />

Contoh 5.7<br />

dy<br />

Tentukan jika y = (4x 3 + 5x 2 – x + 4) 3<br />

dx<br />

Penyelesaian :<br />

Misal u = 4x 3 + 5x 2 – x + 4 y = u 3<br />

du<br />

dx = 12x + 10x − 1 dy<br />

du = 3u<br />

dy<br />

dx = dy du<br />

= 3u (12x + 10x − 1)<br />

du dx<br />

= 3(12x + 10x − 1)(4x + 5x − x + 4)<br />

Soal-soal<br />

Tentukan turunan pertama dari fungsi-fungsi berikut!<br />

1. f(t) = at − bt + 7 6. f(x) = 5 4x<br />

− √3x<br />

4x 5 + 1 x<br />

3<br />

2. f(x) = 3x + 5x<br />

3. g(x) = 2 x + x 2<br />

4. h(x) = 4x<br />

5 + 1 x<br />

7. g(t) = (at + bt + c) (3at − 7)<br />

8. h(w) = b − aw<br />

w + c<br />

(at − bt)<br />

9. v(t) =<br />

(ct − d)<br />

5. w(x) = 7 (2t + 3)<br />

− √2x + 3 10. g(t) = t<br />

4x t − 3<br />

5.6 Turunan fungsi-fungsi trigonometri<br />

y = f(x) = sin x , maka dy = f'(x) = cos x (5.13)<br />

dx<br />

Bukti<br />

dy<br />

= f'(x) = lim<br />

dx D ®<br />

= lim<br />

D ®<br />

= lim<br />

D ®<br />

f(x + Dx) − f(x)<br />

Dx<br />

= lim<br />

D ®<br />

sin x cos Dx + cos x sinDx − sin x<br />

Dx<br />

sin x (cos Dx − 1) + cos x sinDx<br />

Dx<br />

sin(x + Dx) − sin x<br />

Dx<br />

= lim<br />

D ®<br />

(cos Dx − 1) sin Dx<br />

sin x + cos x<br />

Dx<br />

Dx<br />

101

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