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# log help needed Watch

1. write 3log5-log2 as a single logarithm

do i do 5log3-log2
so 15log-log2

so log7.5? is this right
2. (Original post by dongonaeatu)
write 3log5-log2 as a single logarithm

do i do 5log3-log2
so 15log-log2

so log7.5? is this right
No, as you haven't applied the log rules correctly.

alnb = ln(b^a)
lnc - lnd = ln(c/d)
3. (Original post by dongonaeatu)
write 3log5-log2 as a single logarithm

do i do 5log3-log2
so 15log-log2

so log7.5? is this right
Remember,
4. (Original post by TGH1)
No, as you haven't applied the log rules correctly.

alnb = ln(b^a)
lnc - lnd = ln(c/d)
5. (Original post by TGH1)
No, as you haven't applied the log rules correctly.

alnb = ln(b^a)
lnc - lnd = ln(c/d)
The OP looks to have been stuck on a C2 question so it was better not to use the natural log.
6. (Original post by raheem94)
Remember,
7. (Original post by dongonaeatu)
Yeah
8. (Original post by dongonaeatu)
No, 5log3 = log(3^5) = log(243)

you have done log(5^3) which is incorrect.
9. (Original post by raheem94)
Yeah
sorry to keep bothering you.
if log10 a=4.1 find the value of a (1mark)

is it just a=4.1/log10?
10. (Original post by The Mr Z)
No, 5log3 = log(3^5) = log(243)

you have done log(5^3) which is incorrect.
the question was 3log5 not 5log3
11. (Original post by dongonaeatu)
the question was 3log5 not 5log3
good point, in which case also check the second line of your first post - it's good to be consistent

then log 62.5 is correct
12. (Original post by dongonaeatu)
sorry to keep bothering you.
if log10 a=4.1 find the value of a (1mark)

is it just a=4.1/log10?
Remember,
13. (Original post by raheem94)
Remember,
10^4.1=a?

or is it log10^4.1=a
14. (Original post by dongonaeatu)
10^4.1=a?
Correct.
15. (Original post by raheem94)
Correct.
if i do 10^4.1= 12589.25412

if i do log10^4.1= 0.6127838567 which one is it
16. (Original post by dongonaeatu)
if i do 10^4.1= 12589.25412

if i do log10^4.1= 0.6127838567 which one is it
17. (Original post by raheem94)
thanks
18. (Original post by dongonaeatu)
thanks
No problem
19. (Original post by raheem94)
No problem
evaluate log3 1/9.... im pretty sure this is -2? as 3^2 is 9 and because its 1/9 its am minus so am i correct in saying the answer is -2
20. (Original post by dongonaeatu)
evaluate log3 1/9.... im pretty sure this is -2? as 3^2 is 9 and because its 1/9 its am minus so am i correct in saying the answer is -2

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