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Differentiation question

2024 · 27 Jan · Shift 1 · Q53
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  5. /2024 · 27 Jan · Shift 1 · Q53

Differentiation question

2024 · 27 Jan · Shift 1 · Q53

JEE MainMathematicsDifferentiationNumerical+4 / −1
Let f(x)=x3+x2f′(1)+xf′′(2)+f′′′(3),x∈Rf(x)=x^3+x^2 f^{\prime}(1)+x f^{\prime \prime}(2)+f^{\prime \prime \prime}(3), x \in \mathbf{R}f(x)=x3+x2f′(1)+xf′′(2)+f′′′(3),x∈R. Then f′(10)f^{\prime}(10)f′(10) is equal to ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 202

  1. We are given f(x)=x3+x2f′(1)+xf′′(2)+f′′′(3).f(x)=x^3+x^2 f'(1)+x f''(2)+f'''(3).f(x)=x3+x2f′(1)+xf′′(2)+f′′′(3).

Let A=f′(1),B=f′′(2),C=f′′′(3).A=f'(1), \quad B=f''(2), \quad C=f'''(3).A=f′(1),B=f′′(2),C=f′′′(3). Then f(x)=x3+Ax2+Bx+C.f(x)=x^3+Ax^2+Bx+C.f(x)=x3+Ax2+Bx+C.

So f(x)f(x)f(x) is a cubic polynomial.

  1. Differentiate: f′(x)=3x2+2Ax+B,f'(x)=3x^2+2Ax+B,f′(x)=3x2+2Ax+B, f′′(x)=6x+2A,f''(x)=6x+2A,f′′(x)=6x+2A, f′′′(x)=6.f'''(x)=6.f′′′(x)=6.

Hence C=f′′′(3)=6.C=f'''(3)=6.C=f′′′(3)=6.

  1. Now use the definitions of AAA and BBB.

Since A=f′(1)A=f'(1)A=f′(1), A=3(1)2+2A(1)+B=3+2A+B.A=3(1)^2+2A(1)+B=3+2A+B.A=3(1)2+2A(1)+B=3+2A+B. So A=3+2A+B \implies A+B=-3. \tag{1}

Since B=f′′(2)B=f''(2)B=f′′(2), B=6(2)+2A=12+2A. \tag{2}

Substitute (2) into (1): A+(12+2A)=−3A+(12+2A)=-3A+(12+2A)=−3 3A+12=−33A+12=-33A+12=−3 3A=−153A=-153A=−15 A=−5.A=-5.A=−5.

Then B=12+2(−5)=2.B=12+2(-5)=2.B=12+2(−5)=2.

  1. Therefore f′(x)=3x2+2(−5)x+2=3x2−10x+2.f'(x)=3x^2+2(-5)x+2=3x^2-10x+2.f′(x)=3x2+2(−5)x+2=3x2−10x+2.

Now evaluate at x=10x=10x=10: f′(10)=3(10)2−10(10)+2=300−100+2=202.f'(10)=3(10)^2-10(10)+2=300-100+2=202.f′(10)=3(10)2−10(10)+2=300−100+2=202.

Therefore, the required integer is 202.\boxed{202}.202​.

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