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JEE Advanced 2012Paper 1
Exam
JEE Advanced
Year
2012
Paper
Paper 1
Subject
Mathematics
Chapter
Functions

JEE Advanced 2012 · Paper 1 · Mathematics · Functions

The function f:[0,3] arrow[1,29] , defined by f(x)=2 x^ 3 -15 x^ 2...

The function f:[0,3]→[1,29]f:[0,3] \rightarrow[1,29], defined by f(x)=2x3−15x2+36x+1f(x)=2 x^{3}-15 x^{2}+36 x+1, is

Options

  1. Aone-one and onto
  2. Bonto but not one-one
  3. Cone-one but not onto
  4. Dneither one-one nor onto

Correct answer

B. onto but not one-one

Step-by-step solution

Given : f(x)=2x3−15x2+36x+1f(x)=2 x^{3}-15 x^{2}+36 x+1 ⇒f′(x)=6x2−30x+36\Rightarrow f^{\prime}(x)=6 x^{2}-30 x+36 =6=6\left(x^{2}-5 x+6\right)=6(x-2)(x-3) \because f^{\prime}(x)>0 \forall x \in[0,2)andf′(x)<0∀x∈(2,3)and f^{\prime}(x) < 0 \forall x \in(2,3) ∴f(x)\therefore f(x) is increasing on [0,2)[0,2) and decreasing on (2,3)(2,3) ∴f(x)\therefore \quad f(x) is many one on [0,3][0,3] Also f(0)=1,f(2)=29,f(3)=28f(0)=1, f(2)=29, f(3)=28 ∴\therefore \quad Absolute min =1=1 and Absolute max =29=29 ∴\therefore \quad Range of f=[1,29]=f=[1,29]= codomain Hence ff is onto.
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