Question

log2(5x^2-8x)=2
find x

Answer 1

question...are you allowed to use a calculator or no?

Answer 2

no

Answer 3

anybody know?

Answer 4

apply base 2 exponential to both sides, it cancels the log

5x^2-8x=2^2

Answer 5

so square both sides? i don't understand?

Answer 6

hang on it looks like this right

\[\log _{2}(5x^{2}-8x)=2\]

Answer 7

yes

Answer 8

Alright, your log base is 2, to undo that you do this

\[\large 2^{\log_{2}(5x^{2}-8x)}=2^2\]

Answer 9

the left 2 and log2 cancel out and leaves

5x^2-8x=4

Answer 10

x= 12/5?

Answer 11

No, move the 4 over

5x^2-8x-4=0

it factors as (x-2)(5x+2)

so solve x-2=0 and 5x+2=0

Answer 12

x = 2 , x = -2/5

Answer 13

Right