Why cant I solve a hidden quadratic with Logarithms?

Watch
hazlock
Badges: 7
Rep:
?
#1
Report Thread starter 2 years ago
#1
If I have 4^x + 2^x = 12 why cant I just take logs to solve,
why must I recognise there is a hidden quadratic here?
0
reply
Hammad(214508)
Badges: 18
Rep:
?
#2
Report 2 years ago
#2
You can take log of each side here, if you do you have to do it to the WHOLE side, e.g. log(4^x + 2^x) = log(12). This is something you can't solve.
The same think happens when you square. e.g. 4 + 2 = 6 is not 4^2 + 2^2 = 6^2. it's (4+2)^2 = 6^2
1
reply
Hammad(214508)
Badges: 18
Rep:
?
#3
Report 2 years ago
#3
if you do log(4^x) + log(2^x) it's wrong
1
reply
BobbJo
Badges: 12
Rep:
?
#4
Report 2 years ago
#4
The log of a sum is not the sum of the logs, i.e log(4^x + 2^x) =/= log(4^x) + log(2^x)
1
reply
the bear
Badges: 20
Rep:
?
#5
Report 2 years ago
#5
log ( A + B ) ≠ log A + logB
0
reply
S.H.Rahman
Badges: 15
Rep:
?
#6
Report 2 years ago
#6
Not sure if you already know the answer or not but I'll you a hint towards the solution just in case xD

4 = 2^2
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Current uni students - are you thinking of dropping out of university?

Yes, I'm seriously considering dropping out (10)
18.18%
I'm not sure (2)
3.64%
No, I'm going to stick it out for now (16)
29.09%
I have already dropped out (2)
3.64%
I'm not a current university student (25)
45.45%

Watched Threads

View All