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junior college 2 | H2 Maths
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Nelson Loo
Nelson Loo

junior college 2 chevron_right H2 Maths chevron_right Singapore

Does anyone knows how to get the value of 4?

Date Posted: 3 years ago
Views: 591
J
J
3 years ago
Explanation :


Let g(x) = ∫ f(x) dx

Then g'(x) = f(x)


For g(4ln(x)) , apply chain rule.

g'(4ln(x)) = f(4ln(x)) · d/dx (4ln(x))

= f(4ln(x)) · (4/x)

= 4 f(4ln(x)) / x


So,

∫₁ᵉ² f(4ln(x)) / x dx

= ¼ ∫₁ᵉ² 4 f(4ln(x)) / x dx

= ¼ [g(4ln(x))]₁ᵉ²

= ¼ [ g(4ln(e²)) - g(4ln(1)) ]

= ¼ [ g(8) - g(0) ]

= ¼ ∫₀⁸ f(x) dx

= ¼ (16)

= 4
J
J
3 years ago
Alternatively,

∫₁ᵉ² f(4ln(x)) / x dx

= ¼ ∫₁ᵉ² f(4ln(x)) · 4/x dx

= ¼ [F(4ln(x))]₁ᵉ²

= ¼ [F(4ln(e²)) - F(4ln(1))]

= ¼ [F(8) - F(0)]

= ¼ ∫₀⁸ f(x) dx

= ¼ (16)

= 4

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Lee
Lee's answer
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Hope this helps
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Eric Nicholas K
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