dont laugh (1 Viewer)

[crammy90]

i know this should be an easy question. I got it the first time using heaps of logs n what not lol but the answers did it really simply

given 5^m = 4, find the value of 5^1-2m

answer:
5^m = 4
therefore: 5^1-2m = 5/5^2m <--how do they get this lol :S
= 5/(15^m)^2
= 5/16

 

[dolbinau]

5^1-2m

= 5.5^1-2m

= 5/5^2m

Because say x^-1 = 1/x^1


Remember that x^2*x^3= x^5 (you add them). That is why is can be separated. (5^(1-2m))

 

[crammy90]

5^1-2m

= 5.5^1-2m

= 5/5^2m

Because say x^-1 = 1/x^1


Remember that x^2*x^3= x^5 (you add them). That is why is can be separated. (5^(1-2m))

why do u multiply by 5 in the second line :S
i understand it is saying:
5^1-2m

=5^-2m (do we diregard the 1?:S)
= 1/5^2m
but i dont know where the 5 comes from for the numberator

 

[dolbinau]

We don't disregard the 1, that is why there is a 5 on the top

5^(1-2m)

Is the same as

5^1 MULTIPLIED by 5^(-2m)

Remember that when like terms are multiplied, you add their powers.

 

[crammy90]

thanks heaps i understand now
just to clarify: if there different terms we multiply indices yeh?
EDIT:
when we do (5^2m)
= (5^m)^2 so we can sub
is this like 5^m x 5^2
which implies we multiply like terms:
or is it like:
5^m x 1^2 and as there different terms we multiply to get 5^2m :S

 

[danz90]

i did it a different way...

i found the value of m= ln4/ln5

then subbed it into 5^(1-2m)
to give me 5/16

 

[crammy90]

i did it a different way...

i found the value of m= ln4/ln5

then subbed it into 5^(1-2m)
to give me 5/16

yeh thats what i did
its a bit longer tho wouldnt you agree

 

[syriangabsta]

i did it a different way...

i found the value of m= ln4/ln5

then subbed it into 5^(1-2m)
to give me 5/16

^^ thats the way i did it...let the calc do the work