mathematics help: Challenging math problem… - Help.com



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Challenging math problem…

See the image below.
R1, h, and w are known. Solve for Theta.

Using simultaneous equations and substitions I get the following equation that needs to be solved for theta:

W= R1 Cos Ѳ + (h + R1 Sin Ѳ) /Tan Ѳ

There are countless other possible substition equation possibilites. I just need something that will tell me what theta is!

This open post was written 9 months, 3 weeks ago | V/U/S: 549, 10, 6 | Edit Post | Leave a reply | Report Post


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kev4238 offline Verified User (10 months, 2 weeks) Long Term User Shouts: 1 #
Raleigh, NC, US | 9 months, 3 weeks ago (4 minutes after post)

what are the actual numbers? (it’s makes things easier)

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reedco offline Verified User (9 months, 3 weeks) Long Term User Shouts: 0 #
Denver, CO, US | 9 months, 3 weeks ago (16 minutes after post)

I need a generic solution, I need to be able to plug in values for R1, h, and w and get a result that is theta.

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kev4238 offline Verified User (10 months, 2 weeks) Long Term User Shouts: 1 #
Raleigh, NC, US | 9 months, 3 weeks ago (19 minutes after post)

oh, wow. that is a tough one. I am an engineering student with a math minor and it would take me forever to solve that one.

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Anonymous edited this post 9 months, 3 weeks ago. Read the previous text »

Challenging math problem…

W= R1 Cos Ѳ + (h + R1 Sin Ѳ) /Tan Ѳ

R1, h, and w are known. Solve for Theta.

Anonymous edited this post 9 months, 3 weeks ago. Read the previous text »

Challenging math problem…

W= R1 Cos Ѳ + (h + R1 Sin Ѳ) /Tan Ѳ

R1, h, and w are known. Solve for Theta.

[URL=http://imageshack.us][IMG]http://img135.imageshack.us/img135/1253/solveforthetafp5.jpg[/IMG][/URL]

Anonymous edited this post 9 months, 3 weeks ago. Read the previous text »

Challenging math problem…

W= R1 Cos Ѳ + (h + R1 Sin Ѳ) /Tan Ѳ

R1, h, and w are known. Solve for Theta.

[IMG]http://img135.imageshack.us/img135/1253/solveforthetafp5.jpg[/IMG]

Anonymous edited this post 9 months, 3 weeks ago. Read the previous text »

Challenging math problem…

W= R1 Cos Ѳ + (h + R1 Sin Ѳ) /Tan Ѳ

R1, h, and w are known. Solve for Theta.

Creal Default offline Verified User (1 year, 11 months) Long Term User Shouts: 2 #
Houston, TX, US | 9 months, 3 weeks ago (3 hours, 41 minutes after post)

I think I’ve got a way of solving this.

You can get the maximum height of the shape by adding h to the sin(theta)*R1:
h + sin(theta)*R1

You can find the width of where the top comes to a point (coming from the right) with w - cos(theta)*R1

Since theta is equal to the arctangent of the total height over the width from the top to the right corner:
arctan( (h + sin(theta)*R1) / (w - cos(theta)*R1) )

I don’t know if you need to simplify it any further, but I think that’s right. Good luck.

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chapo offline Verified User (4 months, 3 weeks) Long Term User Shouts: 0 #
An Unknown Location | 4 months, 3 weeks ago (4 months, 4 weeks after post)

for simplicity: A= cos(theta), B = sin(theta), C = tan (theta) = B/A
You have:
W = RA + (h + RB)/C
W =RA + h/C + RB/C
W = RA +h/(B/A) +(RB)/(B/A)
W = RA +hA/B + + RA
W =2RA +hA/B
WB = 2RAB +hA
WB = A(2RB +hA)
(WB)^2 = [A(2RBg +hA)]^2n

After you square, you going to have sin^2 on the right side and bunch of sin and cos of different power. Use substitution : cos^2 = 1 - sin^2. You are going to end up with sin only. use another substitution sin(theta) = x. You will end up with the polynomial of the power 4. Solve for x and you are done.
I hope it helped

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inf offline Unverified User #
An Unknown Location | 2 months, 1 week ago (7 months, 1 week after post)

You can solve this with numerical methods.

For theta ranging from -180 degrees (-pi) to +180 (pi) you will likely obtain two solutions.

When W start becoming much larger than H and R1 the you will have only one solution.

You can dowload a 2 week demo of MathSolver from www.emptynetworking.com to investigate the solutions. It is an interesting problem. Do you require a module to always provide the positve/negative answer ?

For example if
W=125
R1=76
and H=7
Theta is 0.696220522269859 +/-2*Pi radians

When
W=78
R1=76
and H=7
then theta has 3 solutions:
-0.996871970251585 +/-2*Pi radians
-0.0951939696816245 +/-2*Pi radians
1.06163124029426 +/-2*Pi radians

And as H become larger you end up with one solution again….

If you require the solution as a simple eqaution, sorry…it is one of those difficult ones, like sin(x)=x

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