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Quick p2 log question!!

scottyoneill

how do i find the answer to this

-3=2^x

..my calculator brings up an error when i try to log negative numbers

Reply 1

lgs98jonee

scottyoneill

how do i find the answer to this

-3=2^x

..my calculator brings up an error when i try to log negative numbers

well that is because 2^x will always be +ve so there are no (real) values of x for which the statement is true

Reply 2

Sza

scottyoneill

how do i find the answer to this

-3=2^x

..my calculator brings up an error when i try to log negative numbers

you sure thats the question?

EDIT: Exactly what my fellow above said.

Reply 3

scottyoneill

well the question is solve

4^x - 2^(x+1) - 15 = 0

using u=2^x

so we get

u^2- 2u -15 = 0

then factorise that....
(u+3)(u-5)=0

u=-3 or u=5

then coz u=2^x

-3=2^x and 5=2^x

is that right so far?? maybe i made a mistake thats why i gota log a neg.?