How to solve an equation in excel

[Usman]

I have a curve i did its fitting using excel and got an equation.
y=2E+07x^-2.146

for y=60 what will be the value of x?

How can we solve this equation using excel..
Thanks

 

[NARAYANK991]

Hi Usman ,

More than Excel , this a matter of using mathematics.

2E+07 is just 2 x 10 raised to the power 7 i.e. 20000000 ( 2 followed by 7 zeros ).

x^-2.146 is just 1/(x^2.146) ; a number raised to a negative power is 1 divided by the same number raised to the positive power.

Thus y = 20000000/(x^2.146)

This is the same as x^2.146 = 20000000/y = 20000000/60

If you take the logarithm or the natural logarithm on both sides , you get :

ln(x^2.146) = ln(20000000/60) = 12.7168982692962

ln(a^b) is just b * ln(a) , which in this case means :

ln(x^2.146) is 2.146 * ln(x).

Hence 2.146 * ln(x) = 12.7168982692962

ln(x) = 12.7168982692962/2.146 = 5.92586126248656

Hence x = the number e raised to this power ; to get this in Excel , we use :

=EXP(1)^5.92586126248656 which gives us 374.60092619087

Thus your answer is 374.60092619087

Narayan

 

[Hui]

Using Excel you can setup a formula in a cell
eg:
D3: =2*10^7*C3^-2.146
C3: 1

Then use Data, What If Analysis, Goal Seek
Set Cell: D3
To value: 60
By changing Cell: C3

Excel will now show you the required value in C3 being: 374.5984

Voila

ps: Your next answer will be rounding errors in Narayans work above

 

[Usman]

Thanks everyone..