Q46 / 90 · JEE Main 2021 (31 Aug Shift 2) · Mathematics

The sum of the roots of the equation, x+1-2log23+2x+2log410-2-x=0, is :

  • A
    log214
  • B
    log212
  • C
    log213
  • Correct answer
    D
    log211

Solution

Given, x+1-2log23+2x+2log410-2-x=0

⇒x+1-2log23+2x+2log2210.2x-12x=0

⇒x+1-2log23+2x+log210.2x-12x=0

⇒x+1-2log23+2x+log210.2x-1-log22x=0

⇒x+1-log23+2x2+log210.2x-1-xlog22=0

⇒x+1-log23+2x2+log210.2x-1-x=0

⇒x+1+log210.2x-13+2x2-x=0

⇒1+log210.2x-13+2x2=0

⇒log210.2x-13+2x2=-1

⇒log210.2x-19+2x2+6.2x=log212

⇒10.2x-19+2x2+6.2x=12

⇒210.2x-1=9+2x2+6.2x

⇒2x2-14.2x+11=0

Let 2x=y

⇒y2-14y+11=0

Let roots are y1=2x1 & y2=2x2

Product of roots, y1y2=2x1×2x2=2x1+x2=11

⇒log2x1+x2=log11

⇒x1+x2log2=log11

⇒x1+x2=log11log2

Hence, x1+x2=log211

Hence, the correct answer is option: 'D'.

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