View Full Version : Exponential Equation
LynnM
Oct 5, 2010, 03:13 PM
Can anyone help me with this question:
( [(9^{2x-1}) (3^{3x})^2] / [(27^{x+2})^4] ) = 81^3
I know that x=-19 but I keep getting -1.5 and 8. Step by step would be really appreciated. Thank you.
Unknown008
Oct 6, 2010, 01:59 AM
\frac{(9^{2x-1}) (3^{3x})^2}{(27^{x+2})^4} = 81^3
Okay, put everything to base 3.
\frac{((3^2)^{2x-1}) (3^{3x})^2}{((3^3)^{x+2})^4} = (3^4)^3
Now, work out the powers:
\frac{(3^{4x-2}) (3^{6x})}{(3^{12x+24})} = (3^{12})
Now, you know that (a^x)(a^y) = a^{x+y} and \frac{a^x}{a^y} = a^{x-y}
Apply this:
3^{4x-2 + 6x - 12x - 24} = 3^{12}
Now, simplify:
3^{-2x-26} = 3^{12}
Equate the powers:
-2x - 26 = 12
This gives you:
x = \frac{12 + 26}{-2} = -19
LynnM
Oct 6, 2010, 07:03 AM
Thanks once again! I now see where I was going wrong. After I worked out the powers, instead of adding the top powers, I was trying to multiply them. (Actually, I think I did try to add them at one point but still ended up with the wrong answer!) Oye! Lol!