## clara1223 one year ago question in comments (logarithmic question)

1. clara1223

$\log _{4}(8-x)=3$ a) 56 b) -56 c) -73 d) 4 e) 72

2. Nnesha

convert log to exponential form example |dw:1437344474349:dw|

3. clara1223

@Nnesha thanks! got it.

4. Nnesha

are you sure?? let me know plz

5. clara1223

@Nnesha could you help me with some other logarithmic questions? #1: ln(x)+7=12 a) e^(12)-7 b)5^e c) e^(7)-12 d) 5 e) e^5 #2: $\log _{2}(x)+\log _{2}(x-4)=\log _{2}(12)$ a) x=-2, x=6 b) x=0, x=4 c) x=2, x=-6 d) x=6 e) x=-2

6. Nnesha

alright okay so first one how would you cancel out ln?? do you know?

7. clara1223

no, can you explain it to me?

8. Nnesha

okay to cancel out ln you have to take e both side example $\huge\rm \cancel{e^{\ln}} x = x$

9. Nnesha

for example in this question i have to solve for x ln x = 3 so i would take ln both sides $\huge\rm \color{red}{e}^{\ln} x= \color{ReD}{e}^3$ $\huge\rm \cancel {\color{red}{e}^{\ln}} x= \color{ReD}{e}^3$ answer is x = e^3

10. clara1223

@Nnesha awesome! now could you help me with the last one?

11. Nnesha

you have to apply log property there

12. clara1223

what's log property?

13. Nnesha

mhm you can start log questions without knowing property! :)quotient rule$\huge\rm log_b y - \log_b x = \log_b \frac{ x }{ y}$ to condense you can change subtraction to division product rule $\huge\rm log_b x + \log_b y = \log_b( x \times y )$ addition ----> multiplication

14. clara1223

okay so once i have $\log _{2}(x ^{2}-4x)=\log _{2}(12)$ what do I do?

15. Nnesha

nice so there are same bases both sides you can cancel each other ot $\huge\rm \color{ReD}{log_b }x = \color{red}{\log_b} y$ $\huge\rm\cancel{ \color{ReD}{log_b }}x = \cancel{\color{red}{\log_b}} y$ x=y

16. clara1223

@Nnesha got it! thanks so much for all the help!

17. Nnesha

my pleasure