Question

I'm not good with logs, can someone help me?
log(x+2)+log(x-1)=1

Answer 1

log(x+2)+log(x-1) = log ((x+2)(x-1))
maybe that helps ;P

Answer 2

And perhaps another helpful rule:
if log(a)=b
than 10^b = a

only in the case when 10 is the basenumber of the logaritm, but if it is not stated otherwise it is always 10.

Answer 3

So
(x+2)(x-1) = 10^1
x^2+x-2= 10
x^2+x-12 = 0
Solve for x and find x = -4 and x = 3

Answer 4

but it's equal to one??, in the first line you have the equation equal to 10

Answer 5

I applied the rule I explained in my second post here.
because b is in this case 1, it means that 10^1 = a
a = (x-1)(x+2) in this case

Answer 6

isn't the b 10?

Answer 7

no, the b is equal to the right side in this equation log ((x+2)(x-1)) =1 ...... so it's 1

Answer 8

okay

Answer 9

so if the equation was equal to 2 the b would be 10^2?

Answer 10

log(x)+log(y) = log(x*y)

if log(a)=b
then 10^b = a

only 2 rules I used

Answer 11

yes, indeed than it would be a = 10^2 = 100

Answer 12

:) alright, the answer at the back of the text is just 3, why isn't the -4 acceptable?

Answer 13

oh, right.... a logaritmic can never have a negative number log(-x) is not possible...
as 10^b = a ... a can only become positive in this formula

Answer 14

oh okay, thank you very much