Logarithms :(

• Jul 20th 2009, 09:09 PM
icecreamfrk09
Logarithms :(
I need help with these just cant figure them out

1. 3^(?) =1

2. 3^(?) = 1/3

3.log5 (1/25) =?

4. logx = -0.7
• Jul 20th 2009, 09:17 PM
pickslides
Quote:

Originally Posted by icecreamfrk09
1. 3^(?) =1

$3^x =1$

$\log_3(3^x) =\log_3(1)$

$x =\log_3(1)$

You can also consider $a^0=1$

Quote:

Originally Posted by icecreamfrk09
I
2. 3^(?) = 1/3

this can be the same way as Q1
• Jul 20th 2009, 09:27 PM
pickslides
Quote:

Originally Posted by icecreamfrk09
3.log5 (1/25) =?

$\log_5(\frac{1}{25})$

= $\log_5(5^{-2})$

= $-2\times \log_5(5)$

= $-2\times 1$

= $-2$
• Jul 20th 2009, 09:28 PM
icecreamfrk09
thank you both...so both one and two are the same answer??
• Jul 20th 2009, 09:32 PM
TKHunny
What? How did you draw that conclusion? These are the most fundamental properties. You must know these or you WILL fail your exams.

$3^{1} = 3$
$5^{1} = 5$

$4^{0} = 1$
$6^{0} = 1$

$2^{-1} = 1/2$
$7^{-1} = 1/7$

Look at these until you no longer feel an urge to ask the question about 1 and 2 being the same.
• Jul 20th 2009, 09:36 PM
pickslides
Quote:

Originally Posted by icecreamfrk09

4. logx = -0.7

This question really depends on the logs base, lets try base 10.

$log_{10}(x) = -0.7$

$10^{log_{10}(x)} = 10^{-0.7}$

$x = 10^{-0.7}$
• Jul 20th 2009, 09:46 PM
icecreamfrk09
k thank you tkhunny i understand now
• Jul 20th 2009, 09:48 PM
yeongil
Quote:

Originally Posted by TKHunny
What? How did you draw that conclusion? These are the most fundamental properties. You must know these or you WILL fail your exams.

To expand on this,

$3^{1} = 3$ because $\log_3 3 = 1$
$5^{1} = 5$ because $\log_5 5 = 1$

$4^{0} = 1$ because $\log_4 1 = 0$
$6^{0} = 1$ because $\log_6 1 = 0$

$2^{-1} = 1/2$ because $\log_2 \left(\frac{1}{2}\right) = -1$
$7^{-1} = 1/7$ because $\log_7 \left(\frac{1}{7}\right) = -1$

01
• Jul 21st 2009, 09:33 PM
TKHunny
Quote:

Originally Posted by icecreamfrk09
k thank you tkhunny i understand now

Get used to these two things and you will do well.

1) A Logarithm IS an Exponent.

2) These are equivalent statements, for appropriate a, b, and c

$log_{b}(a)\;=\;c$ and $b^{c}\;=\;a$