Medium MCQ +4 / -1 PYQ · JEE Mains 2020

Let a – 2b + c = 1.

If $$f(x)=\left| {\matrix{ {x + a} & {x + 2} & {x + 1} \cr {x + b} & {x + 3} & {x + 2} \cr {x + c} & {x + 4} & {x + 3} \cr } } \right|$$, then:

  1. A ƒ(50) = 1 Correct answer
  2. B ƒ(–50) = –1
  3. C ƒ(50) = –501
  4. D ƒ(–50) = 501

Solution

R<sub>1</sub> $\to$ R<sub>1</sub> + R<sub>3</sub> – 2R<sub>2</sub> <br><br>f(x) = $$\left| {\matrix{ {a + c - 2b} &amp; 0 &amp; 0 \cr {x + b} &amp; {x + 3} &amp; {x + 2} \cr {x + c} &amp; {x + 4} &amp; {x + 3} \cr } } \right|$$ <br><br>= (a + c – 2b) ((x + 3)<sup>2</sup> – (x + 2)(x + 4)) <br><br>= x<sup>2</sup> + 6x + 9 – x<sup>2</sup> – 6x – 8 = 1 <br><br>$\therefore$ f(x) = 1 <br><br>$\Rightarrow$ f(50) = 1

About this question

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

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