Question

Difficulty: HardRules of Differentiation (Product, Quotient, and Chain Rules)

Given the function y=(x2+1)32x3y = \frac{(x^2 + 1)^3}{2x - 3}, what is the numerical value of dydx\frac{dy}{dx} evaluated at x=2x = 2?

Answer: 50

Answer

The numerical value of dydx\frac{dy}{dx} at x=2x = 2 is 50.
Applying the Quotient Rule dydx=uvuvv2\frac{dy}{dx} = \frac{u'v - uv'}{v^2} along with the Chain Rule to find u(x)=6x(x2+1)2u'(x) = 6x(x^2 + 1)^2, and evaluating all components at x=2x = 2 gives u(2)=125u(2) = 125, u(2)=300u'(2) = 300, v(2)=1v(2) = 1, and v(2)=2v'(2) = 2. Substituting these values yields (300)(1)(125)(2)12=50\frac{(300)(1) - (125)(2)}{1^2} = 50.

Step-by-Step Solution

1
Set up the Quotient Rule components
u(x)=(x2+1)3u(x) = (x^2 + 1)^3 and v(x)=2x3v(x) = 2x - 3
The given expression is a quotient of two functions requiring dydx=uvuvv2\frac{dy}{dx} = \frac{u'v - uv'}{v^2}.
2
Differentiate u(x)u(x) using the Chain Rule and v(x)v(x) using basic power rules
u(x)=6x(x2+1)2u'(x) = 6x(x^2 + 1)^2 and v(x)=2v'(x) = 2
Differentiating the outer power 3 gives 3(x2+1)23(x^2 + 1)^2, and multiplying by the derivative of the inner function (2x)(2x) gives 6x(x2+1)26x(x^2 + 1)^2.
3
Evaluate u(2)u(2), u(2)u'(2), v(2)v(2), and v(2)v'(2)
u(2)=125u(2) = 125, u(2)=300u'(2) = 300, v(2)=1v(2) = 1, and v(2)=2v'(2) = 2
Substituting x=2x = 2 into each function and derivative simplifies calculation of the overall derivative.
4
Substitute values into the Quotient Rule formula
dydxx=2=(300)(1)(125)(2)(1)2=50\left.\frac{dy}{dx}\right|_{x=2} = \frac{(300)(1) - (125)(2)}{(1)^2} = 50
Evaluating u(2)v(2)u(2)v(2)[v(2)]2\frac{u'(2)v(2) - u(2)v'(2)}{[v(2)]^2} yields the exact numerical result.

Key Concept

Combined Application of Quotient Rule and Chain Rule
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