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JEE Main 2020
Differentiation
Differentiation
Easy

Question

Let f(x)=x3+x2f(1)+xf(2)+f(3),xRf(x)=x^3+x^2 f^{\prime}(1)+x f^{\prime \prime}(2)+f^{\prime \prime \prime}(3), x \in \mathbf{R}. Then f(10)f^{\prime}(10) is equal to ____________.

Answer: 3

Solution

f(x)=x3+x2f(1)+xf(2)+f(3)f(x)=3x2+2xf(1)+f(2)f(x)=6x+2f(1)f(x)=6f(1)=5,f(2)=2,f(3)=6f(x)=x3+x2(5)+x(2)+6f(x)=3x210x+2f(10)=300100+2=202\begin{aligned} & f(x)=x^3+x^2 \cdot f^{\prime}(1)+x \cdot f^{\prime \prime}(2)+f^{\prime \prime \prime}(3) \\ & f^{\prime}(x)=3 x^2+2 x f^{\prime}(1)+f^{\prime \prime}(2) \\ & f^{\prime \prime}(x)=6 x+2 f^{\prime}(1) \\ & f^{\prime \prime \prime}(x)=6 \\ & f^{\prime}(1)=-5, f^{\prime \prime}(2)=2, f^{\prime \prime \prime}(3)=6 \\ & f(x)=x^3+x^2 \cdot(-5)+x \cdot(2)+6 \\ & f^{\prime}(x)=3 x^2-10 x+2 \\ & f^{\prime}(10)=300-100+2=202 \end{aligned}

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