Find this logarithmic equation......

[gdogga]

Using the general formula: y=aln(x+b)+c, find a logarithmic equation which passes through the points (0,0) (12,20) (30,30), and is not horizontal at x=30.

[d0minicz]

whats the answer

[gdogga]

No idea, i am completely stuck on it 

[ilovevce]

Substitute in the three points to create three separate equations.

Now solve those equations simultaneously.

[gdogga]

Substitute in the three points to create three separate equations.

Now solve those equations simultaneously.

I tried this, but i still can't solve it, its annoying me so bad

[ilovevce]

It seems quite difficult.

Is this calculator active?

[ilovevce]

1.

2.



3.





Using change of base rule:







See if you can solve it from there.

[/0]

lmfao my calculator can't even solve it

[ilovevce]

I just attempted to solve for b.

You can't do it! When you expand out those brackets in the last step I posted above, you get an irreducible quadratic.

I don't think this has a solution...

[TrueTears]

Are you sure it's right question?

[gdogga]

I end up with:

31B^2 - 39B + 144 = 0

And yes, i am sure this is the right question...

[TrueTears]

Well, you can't solve the quadratic for b. No log graph passes through those points.

[ilovevce]

I realised I made a mistake with my expansion.

You end up with:



Which yield:

and

Only b = 3.175 is valid

[gdogga]

I realised I made a mistake with my expansion.

You end up with:



Which yield:

and

Only b = 3.175 is valid

Thanks Heaps, you are an absolute lifesaver...

[enwiabe]

Boy will he shit bricks when he logs on to find that this thread is here

This is punishment for abusing VN.