How Do You Make 'z' the Subject in This Trigonometric Formula?

  • Thread starter mubashirmansoor
  • Start date
In summary, the conversation is about finding a way to make 'z' the subject of a given formula. The formula is (z-x)/g = tan(0.5(arctan((z-y)/g)+arctan((y-x)/g))). The participants discuss different methods and formulas to solve for z, with one of them making a mistake in writing the formula. Eventually, the correct formula is found to be z = 2x - y +/- sqrt(3y^2-6yx+3x^2-4g^2).
  • #1
mubashirmansoor
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Can you please help me for making 'z' the subject of formula;

(z-x)/g = tan(0.5(arctan((z-y)/g)+arctan((y-x)/g)))

I'll be thankfull...
 
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  • #2
Sometimes it's not possible to make 'z' the subject of a formula.
 
  • #3
mubashirmansoor said:
Can you please help me for making 'z' the subject of formula;

(z-x)/g = tan(0.5(arctan((z-y)/g)+arctan((y-x)/g)))

I'll be thankfull...


ok let's begin by writing that more mathematically.

[tex]\frac{z-x} {g} = tan{\frac{tan^{-1}(\frac{z-y} {g})+tan^{-1}(\frac{y-x} {g})} {2}[/tex]

IS this what you mean? 6am...I might have done it wrong.

tip: maybe trying to get both sides to look messy might help...i have a way to solve this in mind and if it works that way, this is a beautiful problem. if it doesn't... i don't like this problem.
 
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  • #4
Oh I hate you now, it awakened my curiosity and...50 minutes later I think I have it. One Z on the process decided to turn squared on me and instead of a nice common factor i had to use quadratic formula. indication that i did something awfully wrong but...i checked and it looks ok.

EDIT: Ok I re-read the stickies, this isn't the homework section so i can post the work I did. Basically i got rid of that nasty 1/2 by...well this way: (sorry for the notation, i wrote this is a .txt file.

Robokapp's work said:
(z-x)/g = tan(0.5(arctan((z-y)/g)+arctan((y-x)/g)))


2arctan[(z-x)/g] = arctan((z-y)/g)+arctan((y-x)/g)


tan{2arctan[(z-x)/g]} = tan{arctan((z-y)/g)+arctan((y-x)/g)}


Using the double angle formula in first part and angle plus angle formula in second part...
 
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  • #5
thanks robokapp, I'll be thankfull if you do the whole thing (applying the formulas) what is z equal to?

I don't really know which formulas you are talking about...

thanks once again
 
  • #6
Okay...sure. After all I do am curious if I did any horrible mistakes (i might have)

I disliked the 1/2 part. I knew there are formulas for different half-angle, duble angle, angle plus angle etc so i went to wikipedia and typed in 'trigonometry.' the formulas are on bottom.

I knew the "tan" and "arctan" will cancel each other out so I picked formulas so that I only work in terms of tan. This is my full work:

(z-x)/g = tan(0.5(arctan((z-y)/g)+arctan((y-x)/g)))


2arctan[(z-x)/g] = arctan((z-y)/g)+arctan((y-x)/g)


tan{2arctan[(z-x)/g]} = tan{arctan((z-y)/g)+arctan((y-x)/g)}


Using the double angle formula in first part and angle plus angle formula in second part...


2tan{arctan[(z-x)/g]}
----------------------------------------------- =
1 - tan{arctan[(z-x)/g]} * tan{arctan[(z-x)/g]}


tan{arctan((z-y)/g)}+tan{arctan((y-x)/g)}
= -------------------------------------------- ====>
1+tan{arctan((z-y)/g)}*tan{arctan((y-x)/g)}


2(z-x)/g....(z-y)/g+(y-x)/g
-------------- = ------------------- ====>
1-(z-x)^2/g^2...1+(z-y)/g * (y-x)/g


2(z-x)....(z-y)+(y-x)
-------------- = ---------------- =====>
1-(z-x)^2/g...1+(z-y) * (y-x)


2gz-2gx ...z-x
------------- = ---------------- ======> flip it.
g-z^2-2zx+x^2...1+zy-zx-y^2+xy


g-z^2-2zx+x^2...1+zy-zx-y^2+xy
------------- = -------------- =======>
2gz-2gx...z-x


g-z^2-2zx+x^2... 1+zy-zx-y^2+xy
------------- = -------------- =======> multiply second by 2g/2g
2g(z-x)..... z-x


g-z^2-2zx+x^2...2g(1+zy-zx-y^2+xy)
------------- = ------------------- =======>
2g(z-x).....2g(z-x)


g-z^2-2zx+x^2 = 2g+2zgy-2zgx-2gy^2+2gxy


-z^2-2zx-2zgy-2zgx = 2g+2gxy-2gy^2-g-x^2


-z^2-2zx-2zgy-2zgx = g+2gxy-2gy^2-x^2


-z^2+z(2x-2gy-2gx) - g-2gxy+2gy^2+x^2 = 0


Calling

a= -1
b= 2x-2gy-2gx
c= -g-2gxy+2gy^2+x^2


z=0.5{-(2x-2gy-2gx) +/- sqrt[(2x-2gy-2gx)^2+4(-g-2gxy+2gy^2+x^2)]}


-------------------------------------------

Now...I don't think it should have 2 answers, I don't seem to have any way around that z^2 however.


The ... takes place of..balnk so numbers don't run into each other.

please someone check my work...
 
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  • #7
Thanks Robokapp, I had actually done a sily mistake in writing the question, It should had been:

(z-x)/2g = tan(0.5(arctan((z-y)/g)+arctan((y-x)/g)))

But I used the formulas you provided and got the following results:

z = 2x - y +/- sqrt(3y^2-6yx+3x^2-4g^2)

Thankyou you were a great help
 
  • #8
but chk it out, Did I do it correctly? becase I'm little puzzeled It's not working as I wanted...
 

FAQ: How Do You Make 'z' the Subject in This Trigonometric Formula?

How do I make z the subject of a formula?

To make z the subject of a formula, you need to isolate z on one side of the equation. This can be done by using algebraic operations such as addition, subtraction, multiplication, and division to move all other variables and numbers to the other side of the equation.

What is the purpose of making z the subject of a formula?

The purpose of making z the subject of a formula is to solve for the value of z. This is useful in many scientific and mathematical applications, as it allows you to find a specific unknown variable in a given equation.

What should I do if z is on both sides of the equation?

If z is on both sides of the equation, you can still make it the subject by combining like terms on one side and then using algebraic operations to isolate z on that side. This may involve factoring or distributing to simplify the equation.

Can I use the same method for making any variable the subject of a formula?

Yes, the same method can be used for making any variable the subject of a formula. The key is to isolate the variable on one side of the equation by using algebraic operations to move all other variables and numbers to the other side.

Is there a specific order in which I should perform algebraic operations when making z the subject of a formula?

There is no specific order in which you must perform algebraic operations when making z the subject of a formula. You can choose the most efficient method based on the given equation, but it is important to perform the same operation on both sides of the equation to maintain balance.

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