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Jika f(x)=(2x−1)² (x+2), maka f′(x)=…
Jawaban yang benar f'(x) = 12x² + 8x – 7.
Sifat :
y = (f(x))ⁿ maka y’ = f'(x) · n · (f(x))^(n-1)
y = a x maka y’ = a
y = a maka y’ = 0
y = u · v maka y’ = u’·v + u·v’
(a + b)(c – d) = ac – ad + bc – bd
(a – b)² = a² – 2ab + b²
f(x) = (2x – 1)² (x + 2)
u = (2x – 1)²
u’ = 2 · 2 · (2x – 1)
u’ = 4(2x – 1)
v = x + 2 —> v’ = 1
f'(x) = u’·v + u·v’
= 4(2x – 1)(x + 2) + (2x – 1)²(1)
= 4(2x² + 4x – x – 2) + 4x² – 4x + 1
= 4(2x² + 3x – 2) + 4x² – 4x + 1
= 8x² + 12x – 8 + 4x² – 4x + 1
= 12x² + 8x – 7
Jadi, f'(x) = 12x² + 8x – 7.