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JEE Main 2020
Differentiation
Differentiation
Easy

Question

If f(x)=x3x2f(1)+xf(2)f(3),xRf(x) = {x^3} - {x^2}f'(1) + xf''(2) - f'''(3),x \in \mathbb{R}, then

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Solution

f(x)=x3x2f(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 R Let f(1)=a,f(2)=b,f(3)=c\mathrm{f}^{\prime}(1)=\mathrm{a}, \mathrm{f}^{\prime \prime}(2)=\mathrm{b}, \mathrm{f}^{\prime \prime \prime}(3)=\mathrm{c} f(x)=x3ax2+bxcf(x)=3x22ax+bf(x)=6x2af(x)=6c=6,a=3,b=6f(x)=x33x2+6x6f(1)=2,f(2)=2,f(3)=12,f(0)=62f(0)f(1)+f(3)=2=f(2)\begin{aligned} & f(x)=x^3-a x^2+b x-c \\\\ & f^{\prime}(x)=3 x^2-2 a x+b \\\\ & f^{\prime \prime}(x)=6 x-2 a \\\\ & f^{\prime \prime \prime}(x)=6 \\\\ & c=6, a=3, b=6 \\\\ & f(x)=x^3-3 x^2+6 x-6 \\\\ & f(1)=-2, f(2)=2, f(3)=12, f(0)=-6 \\\\ & 2 f(0)-f(1)+f(3)=2=f(2) \end{aligned}

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