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MHT CET202523 Apr 2025Evening ShiftMathematicsDifferentiationActual

If f (x)=3 x^3+2 x^2 f ^ (1)+x f ^ (2)+ f ^ (3) then f (x)=

Options

  1. A1 7 (3 x^3-90 x^2+72 x+18 )
  2. B1 7 (21 x^3-90 x^2+72 x+126 )
  3. C3 x^3-90 x^2+72 x+18
  4. D3 x^3-45 x^2+36 x+9

Correct answer

B. 1 7 (21 x^3-90 x^2+72 x+126 )

Step-by-step solution

Let f(x) = 3x^3 + 2x^2 f'(1) + x f''(2) + f'''(3) and define constants A = f'(1) , B = f''(2) , and C = f'''(3) . The function becomes f(x) = 3x^3 + 2Ax^2 + Bx + C . Successive differentiation yields: f'(x) = 9x^2 + 4Ax + B , f''(x) = 18x + 4A , f'''(x) = 18 . Using the definitions of A , B , and C : A = 9 + 4A + B simplifies to -3A - B = 9 , B = 36 + 4A gives -4A + B = 36 , and C = 18 . Solving the system -3A - B = 9 and -4A + B = 36 : Adding the equations eliminates B , resulting in -7A = 45 , so A = - 45 7 . Sub

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