reversing fomula

[mond]

A3 = 52.1847833333333
B3 =(LOG(TAN(RADIANS(A3/2+45))))*7915.704468-(23.0133633*(SIN(RADIANS(A3))))-0.051353*(SIN(RADIANS(A3))^3)-0.000206*(SIN(RADIANS(A3)))^5
So will be B3 = 3665.0338
I wish to reverse the formula by writing on C3 = 3665.0338 and on D3 the answer will be 52.1847833333333
Can anybody please help me.

 

[c_m]

mond,
Welcome to the board.

Instead of reversing the formula, why not just use goalseek?

 

[pedro-egoli]

Mond, I have never used Goal Seek before and am trying to come to grips with it.

Not sure where to put the various figures to come up with the formula.
This was my amateurish attempt

Book1
	A	B	C	D	E
1
2
3	52.1848	3665.03	2557.06	52.1848
Sheet1

Your correction would be appreciated.

Pedro

 

[c_m]

hello Pedro,
why is D3 = C3/49?

 

[c_m]

what I was trying to say with "using goalseek" is:
let C3 be blank or any number (greater than equal to -90 and less than equal to 90) and D3 have this formula:
=(LOG(TAN(RADIANS(C3/2+45))))*7915.704468-(23.0133633*(SIN(RADIANS(C3))))-0.051353*(SIN(RADIANS(C3))^3)-0.000206*(SIN(RADIANS(C3)))^5

now goto Tools>>goal seek>>Select D3 as Set cell>>Type 3665.0338 in To Value>>select C3 as By Changing cell>>click ok>>see the results

 

[pedro-egoli]

Sorry c_m, I typed wrong name in my request.
Mondo that formula was because I thought I had to put any formula and the Goal seek would correct it.

Tried the suggested method but get a message "Goal seeking may not have found a solution"

This is the result on spreadsheet

GoalSeek.xls
	A	B	C	D	E
1
2
3			-335544	-3.81667E-13
Sheet1

I started by inserting formula into D3 , selected Goal Seek and then in "Set cells" i entered D3.
Then typed the 3665 number into "To Value" and selected C3 for "Changing cells".

Where have I gone wrong?

Pedro

 

[pedro-egoli]

PROBLEM SOLVED.
i input the original formula with the reference to A3 . Changed it to C3 and all well .

Thanks

Pedro

 

[c_m]

glad your prob is solved.
Adding to that, it is possible that your goalseek or solver may not find solution to your problem. Its typical with non-linear composite functions. In this case, the solutions may have 5 real roots...so goalseek or solver may return any of the roots if the initial value is fairly close or in neighborhood of the root....otherwise it may return error of "no solutions found"...In order to get rid of this...i usually use solver with constraints on changing cell so that the solution converges instead of diverging.

 

[pgc01]

Hi

This expression deals with trigonometric functions and may have an infinite number of solutions.

For ex., base on the solution 52.1847833333333 any number

52.1847833333333 + 360 * K

where K is any integer, positive or negative, ex:

K=1  solution: 412.1847833
K=-1 solution: -307.8152167

are also solutions.

 

[mond]

hello there,
thanks for the immediate response to my problem, but what i liked to change is the formula on d3, which is the reverse formula on b3 so it will give answer base on c3 value.

thanks again.