Math Is Fun Forum

Kingston

Member

Registered: 2008-06-15

Posts: 2

lLOGRITHMIC EQUATIONS

Does anyone know how to solve these types of problems?

logx+log(x+6)=2

I am completely lost.

Thanks _ Bob

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: lLOGRITHMIC EQUATIONS

The two logs on the left can be combined into log(x(x+6)).
Then make both sides a power of 10 to get x(x+6) = 100, and solve the quadratic equation.

(I'm assuming both the logs are in base 10. If they're not it's still solvable, the method will just be a bit different.)

---

Why did the vector cross the road?
It wanted to be normal.

Kingston

Member

Registered: 2008-06-15

Posts: 2

Re: lLOGRITHMIC EQUATIONS

Thank you I understand that part but when I do that and apply the Quadratic formula, I do not get anywhere near the answer my textbook has.  There answer is X= 7.440307.

Here is my work:

x(x+6)=100
x^2+6x-100=0

a=1  b=6  c=-100

-6+or- sqr 6^2-4(1)(-100)/2=20.38

Do you know where I have gone wrong
ty

Bob

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: lLOGRITHMIC EQUATIONS

Thank you I understand that part but when I do that and apply the Quadratic formula, I do not get anywhere near the answer my textbook has.  There answer is X= 7.440307.

Here is my work:

x(x+6)=100
x^2+6x-100=0

a=1  b=6  c=-100

-6+or- sqr 6^2-4(1)(-100)/2=20.38

Do you know where I have gone wrong
ty

Bob

You've just typed it in your calculator incorrectly. Make sure you get your order of operations right: