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NCERT Exemplar · Q39

Q.Differentiate with respect to xx: (2x−7)2(3x+5)3(2x - 7)^2 (3x + 5)^3.

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To differentiate the product of two composite functions, we apply the Product Rule first, and then use the Chain Rule for differentiating each individual factor. The derivative of (2x−7)2(3x+5)3(2x - 7)^2 (3x + 5)^3 is (2x−7)(3x+5)2(30x−43)\boxed{(2x - 7)(3x + 5)^2 (30x - 43)}.

When we need to differentiate a function that is a product of two other functions, say y=u(x)⋅v(x)y = u(x) \cdot v(x), the standard approach is to use the Product Rule. In this specific problem, each of the functions u(x)=(2x−7)2u(x) = (2x - 7)^2 and v(x)=(3x+5)3v(x) = (3x + 5)^3 is itself a composite function (a function raised to a power), meaning we will also need to apply the Chain Rule when finding u′(x)u'(x) and v′(x)v'(x).

The Product Rule allows us to break down the differentiation of a complex product into simpler parts. It essentially says that the rate of change of a product is the rate of change of the first function times the second function, plus the first function times the rate of change of the second function.

Here's how we apply this to the given problem:

  1. Identify the two functions in the product.

    Let y=(2x−7)2(3x+5)3y = (2x - 7)^2 (3x + 5)^3.

    We can define u=(2x−7)2u = (2x - 7)^2 and v=(3x+5)3v = (3x + 5)^3.

    Our goal is to find dydx\frac{dy}{dx}.

  2. Recall the Product Rule.

    If y=u⋅vy = u \cdot v, then dydx=u′v+uv′\frac{dy}{dx} = u'v + uv'.

    Here, u′u' denotes dudx\frac{du}{dx} and v′v' denotes dvdx\frac{dv}{dx}.

  3. Differentiate uu with respect to xx.

    u=(2x−7)2u = (2x - 7)^2. This is a composite function of the form f(g(x))f(g(x)), where f(x)=x2f(x) = x^2 and g(x)=2x−7g(x) = 2x - 7.

    We use the Chain Rule: dudx=f′(g(x))⋅g′(x)\frac{du}{dx} = f'(g(x)) \cdot g'(x).

    f′(x)=2xf'(x) = 2x, so f′(g(x))=2(2x−7)f'(g(x)) = 2(2x - 7).

    g′(x)=ddx(2x−7)=2g'(x) = \frac{d}{dx}(2x - 7) = 2.

    Therefore, u′=2(2x−7)⋅2=4(2x−7)u' = 2(2x - 7) \cdot 2 = 4(2x - 7).

  4. Differentiate vv with respect to xx.

    v=(3x+5)3v = (3x + 5)^3. This is also a composite function, with f(x)=x3f(x) = x^3 and g(x)=3x+5g(x) = 3x + 5.

    Using the Chain Rule: dvdx=f′(g(x))⋅g′(x)\frac{dv}{dx} = f'(g(x)) \cdot g'(x).

    f′(x)=3x2f'(x) = 3x^2, so f′(g(x))=3(3x+5)2f'(g(x)) = 3(3x + 5)^2.

    g′(x)=ddx(3x+5)=3g'(x) = \frac{d}{dx}(3x + 5) = 3.

    Therefore, v′=3(3x+5)2⋅3=9(3x+5)2v' = 3(3x + 5)^2 \cdot 3 = 9(3x + 5)^2. …

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