Medium MCQ +4 / -1 PYQ · JEE Mains 2022

$$ \text { Let } f(x)=a x^{2}+b x+c \text { be such that } f(1)=3, f(-2)=\lambda \text { and } $$ $f(3)=4$. If $f(0)+f(1)+f(-2)+f(3)=14$, then $\lambda$ is equal to :

  1. A $-$4
  2. B $\frac{13}{2}$
  3. C $\frac{23}{2}$
  4. D 4 Correct answer

Solution

<p>$f(1) = a + b + c = 3$ ..... (i)</p> <p>$f(3) = 9a + 3b + c = 4$ .... (ii)</p> <p>$f(0) + f(1) + f( - 2) + f(3) = 14$</p> <p>OR $c + 3 + (4a - 2b + c) + 4 = 14$</p> <p>OR $4a - 2b + 2c = 7$ ..... (iii)</p> <p>From (i) and (ii) $8a + 2b = 1$ ..... (iv)</p> <p>From (iii) $- (2) \times$ (i)</p> <p>$\Rightarrow 2a - 4b = 1$ ..... (v)</p> <p>From (iv) and (v) $a = {1 \over 6},\,b = {{ - 1} \over 6}$ and $c = 3$</p> <p>$f( - 2) = 4a - 2b + c$</p> <p>$= {4 \over 6} + {2 \over 6} + 3 = 4$</p>

About this question

Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations

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