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# C2- Logarithms question Watch

1. if you solve the logarithms equation :

log4x + 2logx4 + 3 = 0

to get y= -1 or y= -2

were log4 x can equal -1 or -2

then how come if you solve the equation

2(to the power of 2x) + 3(2(to the power of x) ) - 4 = 0

to get y = -4 or y= 1

y and hence log10(2 to the power of x) can't equal -4 ??

its probably a really stupid question but i just don't understand so any help would be appreciated
2. It is not at all a stupid question...

the two negative values from the first equation are logarithms... they can be negative... for instance Log0.1 is -1...

in the second equation you must reject the negative answer and only keep the positive answer... because 2 to any power is always greater than zero...

if you look at the two graphs you will see what i mean...

the bear

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3. (Original post by the bear)
It is not at all a stupid question...

the two negative values from the first equation are logarithms... they can be negative... for instance Log0.1 is -1...

in the second equation you must reject the negative answer and only keep the positive answer... because 2 to any power is always greater than zero...

if you look at the two graphs you will see what i mean...

the bear

oh so its because in y= log4 x, y = the power which can be positive or negative.

I understand now thank you!

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Updated: December 28, 2010
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