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Worked Examples · Example 12

Q.Differentiate with respect to xx:

(i) y=e3x2−1y = e^{3x^{2}-1}
(ii) y=ln⁡(4x3+2x)y = \ln(4x^{3}+2x).
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(i) y=e3x2−1y=e^{3x^2-1}. Let u=3x2−1u=3x^2-1 (inner), so y=euy=e^{u} (outer). Then dydu=eu\dfrac{dy}{du}=e^{u} and dudx=6x\dfrac{du}{dx}=6x (power rule on 3x23x^2, derivative of −1-1 is 00). By the chain rule:

dydx=dydu⋅dudx=eu⋅6x=6x e3x2−1.\frac{dy}{dx} = \frac{dy}{du}\cdot\frac{du}{dx} = e^{u}\cdot6x = 6x\,e^{3x^{2}-1}.

(ii) y=ln⁡(4x3+2x)y=\ln(4x^3+2x). Let u=4x3+2xu=4x^3+2x (inner), so y=ln⁡uy=\ln u (outer). Then dydu=1u\dfrac{dy}{du}=\dfrac1u and dudx=12x2+2\dfrac{du}{dx}=12x^{2}+2 (power rule on each term). By the chain rule:

dydx=dydu⋅dudx=1u⋅(12x2+2)=12x2+24x3+2x.\frac{dy}{dx} = \frac{dy}{du}\cdot\frac{du}{dx} = \frac{1}{u}\cdot(12x^{2}+2) = \frac{12x^{2}+2}{4x^{3}+2x}. …

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