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Derivative of a composite quotient using chain and quotient rule

Let f(x)=ex2(x+1)4.f(x) = \dfrac{e^{x^2}}{(x+1)^4}. Find f′(0)f'(0).

Hint

Use the quotient rule with numerator u=ex2u = e^{x^2} and denominator v=(x+1)4v = (x+1)^4. To find u′u', apply the chain rule since ex2e^{x^2} is a composite function with outer function e(⋅)e^{(\cdot)} and inner function x2x^2.

Step-by-step solution

Let u=ex2u = e^{x^2} and v=(x+1)4v = (x+1)^4. By the chain rule, u′=ex2⋅2xu' = e^{x^2}\cdot 2x, and by the power/chain rule, v′=4(x+1)3v' = 4(x+1)^3. By the quotient rule, f′(x)=u′v−uv′v2=2xex2(x+1)4−ex2⋅4(x+1)3(x+1)8f'(x) = \dfrac{u'v - uv'}{v^2} = \dfrac{2x e^{x^2}(x+1)^4 - e^{x^2}\cdot 4(x+1)^3}{(x+1)^8}.

Now substitute x=0x=0: u(0)=e0=1u(0) = e^0 = 1, u′(0)=2(0)e0=0u'(0) = 2(0)e^0 = 0, v(0)=14=1v(0) = 1^4 = 1, and v′(0)=4(1)3=4v'(0) = 4(1)^3 = 4. So f′(0)=u′(0)v(0)−u(0)v′(0)v(0)2=0⋅1−1⋅412=−4f'(0) = \dfrac{u'(0)v(0) - u(0)v'(0)}{v(0)^2} = \dfrac{0\cdot 1 - 1\cdot 4}{1^2} = -4.

Identifying the outer function in the composite numerator

Hint
Step-by-step solution

The outer function is the exponential function, written as e to the something. The inner function was x squared, which gets plugged into the outer exponential function. Recognizing this split was necessary to apply the chain rule and get the derivative two x times e to x squared.

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