Skip to main contentSkip to solution

Suppose, log⁡3x=log⁡12y=a\log_3 x = \log_{12} y = a, where x,yx, y are positive numbers. If GG is the geometric mean of x and y, and log⁡6G\log_6 G is equal to

Solution

✅ Correct Option: 4

We have: log⁡3x=log⁡12y=a\log_3 x = \log_{12} y = a

This means both logarithmic expressions equal the same value aa.


If log⁡bm=n\log_b m = n, then bn=mb^n = m

From log⁡3x=a\log_3 x = a:

x=3ax = 3^a

From log⁡12y=a\log_{12} y = a:

y=12ay = 12^a


Now we can find xyxy:

xy=3a×12axy = 3^a \times 12^a

Using the exponent rule am×bm=(ab)ma^m \times b^m = (ab)^m:

xy=3a×12a=(3×12)a=36axy = 3^a \times 12^a = (3 \times 12)^a = 36^a


The geometric mean of two positive numbers is the square root of their product.

For numbers xx and yy: G=xyG = \sqrt{xy}

G=xy=36aG = \sqrt{xy} = \sqrt{36^a}

Since n=n1/2\sqrt{n} = n^{1/2}:

G=36a=(36a)1/2G = \sqrt{36^a} = (36^a)^{1/2}

Using the exponent rule (am)n=amn(a^m)^n = a^{mn}:

G=(36a)1/2=36a/2G = (36^a)^{1/2} = 36^{a/2}


Notice that 36=6236 = 6^2, so:

G=36a/2=(62)a/2G = 36^{a/2} = (6^2)^{a/2}

G=(62)a/2=62×a/2=6aG = (6^2)^{a/2} = 6^{2 \times a/2} = 6^a


We need to find log⁡6G\log_6 G where G=6aG = 6^a.

Using the property log⁡b(bx)=x\log_b(b^x) = x:

log⁡6G=log⁡6(6a)=a\log_6 G = \log_6(6^a) = a


log⁡6G=a\log_6 G = a

The beauty of this problem is that despite the different bases (3, 12, and 6), the common value aa ties everything together through the properties of logarithms and exponents.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question