Verified Solution • 2025–26 Session moderate

QJEEM24Ma5830: JEE Main 2024 Mathematics - Class 11 JEEM24Ma5830 Solution: The sum of all the solutions of the equation is :

The sum of all the solutions of the equation (8)2x−16⋅(8)x+48=0(8)^{2 x}-16 \cdot(8)^x+48=0 is :

Multiple Choice Options

  • A 1+log⁡8(6)1+\log _8(6)
  • B 1+log⁡6(8)1+\log _6(8)
  • C log⁡8(6)\log _8(6)
  • D log⁡8(4)\log _8(4)

Step-by-Step Verified Solution

First, let's start by substituting y=(8)xy = (8)^x in the given equation. By substituting, the equation 82x−16⋅8x+48=08^{2x} - 16 \cdot 8^x + 48 = 0 will be transformed into

y2−16y+48=0y^2 - 16y + 48 = 0

Now, we have a quadratic equation in yy . To find the roots of this quadratic equation, we can use the quadratic formula:

y=−b±b2−4ac2ay = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

In this case, a=1a = 1 , b=−16b = -16 , and c=48c = 48 . Substituting these values into the formula, we get:

y=16±256−1922y = \frac{16 \pm \sqrt{256 - 192}}{2}

y=16±642y = \frac{16 \pm \sqrt{64}}{2}

y=16±82y = \frac{16 \pm 8}{2}

Solving for the two possible values of yy , we have:

y=16+82=12y = \frac{16 + 8}{2} = 12

y=16−82=4y = \frac{16 - 8}{2} = 4

Now, recall that we substituted y=(8)xy = (8)^x . So, we need to solve for xx when y=12y = 12 and y=4y = 4 :

8x=128^x = 12

x=log⁡8(12)x = \log_8(12)

8x=48^x = 4

x=log⁡8(4)x = \log_8(4)

Therefore, the solutions for xx are log⁡8(12)\log_8(12) and log⁡8(4)\log_8(4) . The sum of these solutions is:

log⁡8(12)+log⁡8(4)\log_8(12) + \log_8(4)

Using the logarithmic property that log⁡b(m)+log⁡b(n)=log⁡b(m⋅n)\log_b(m) + \log_b(n) = \log_b(m \cdot n) , we get:

log⁡8(12)+log⁡8(4)=log⁡8(12⋅4)\log_8(12) + \log_8(4) = \log_8(12 \cdot 4)

=log⁡8(48)= \log_8(48)

Now, we note that:

48=8⋅648 = 8 \cdot 6

Thus,

log⁡8(48)=log⁡8(8⋅6)=log⁡8(8)+log⁡8(6)=1+log⁡8(6)\log_8(48) = \log_8(8 \cdot 6) = \log_8(8) + \log_8(6) = 1 + \log_8(6)

Therefore, the sum of all the solutions of the equation is:

Option A 1+log⁡8(6)1 + \log_8(6) .

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