# Maths

posted by Sanjay

9^x+2 - 6* 3^x+1= 0 find x

1. Reiny

He started by letting u = 3^x

look at the first term 9^(x+2) <--- I will assume those necessary brackets, as did Steve.
9^(x+2) = (3^2)^(x+2)
= 3^(2x + 4)
= 3^2x * 3^4
= 81 * (3^x)^2 , also 6*3^(x+1) = 6*3^x * 3^1 = 18*3^x

so, 9^(x+2) - 6* 3^(x+1) = 0 becomes

81 * (3^x)^2 - 18*3^x = 0
81 u^2 - 18u = 0
9u(9u - 2) = 0
9u = 0 ---> u = 0
or
9u = 2 ---> u = 2/9

so 3^x = 0 , which has no solution

OR

3^x = 2/9
xlog3 = log2 - log9
x = (log2 - log9)/log3 = appr -1.369

This answer can be verified in the original equation

## Similar Questions

1. ### maths

I am really facing difficulty in maths. I do my best to improve in maths but after entering in the examination hall during my exams, i just get confused. please help The proper name for the subject is mathematics or just "math" for …
2. ### bobprsly

I do apologize but I looked in the past post and i don't remember asking about this problem in math. But if i did then I do apologize but i don't remember what you said in as the responce. If you can copy and paste it for me to see. …
3. ### confused

as i earlier posted and , 1 day ago , i am confusesd hw we ll find freezing point......isnt it T pure solvent - T solution .. which ll be 0-(-23.3) = 23.3 plz conform .. and do we have to use Kf.m .. formula in order to get ( -23.3)(1)= …
4. ### Chemistry repost

Whoever you are -- Please DO NOT USE TUTORS' NAMES where your name or nickname should be. ~~~~~~~~~~~~~~~~~~~~~~~~~~ as i earlier posted and , 1 day ago , i am confusesd hw we ll find freezing point......isnt it T pure solvent - T …
5. ### physics

If atmospheric refraction did not occur, how would the apparent time of sunrise and sunset be changed?
6. ### Math-Reiny

I posted this problem earlier and you answered it for me. The teacher said the correct answer is 3+2y/7-4y. How is that the answer. Below is what you did earlier 3/(y+2) / (7/y-4)) = 3/(y+2) * (y-4)/7 = (3y-12)/(7y+14) or 3(y-4)/[7(y+2)]