Ok, im sort of stuck on this. Havent done algebra stuff for awhile and i cant solve this equation.

230=360sin(theta) - 63cos(theta)

trying to get theta

Thanks

42

Man, it's been a LOOOOOOOOOONG time.  I don't remember, either.

Quoted: 42

Yeah, but what's the QUESTION, wiseass?

Hint: Use trig identities.

Quoted: 42

close

i know the answer is approx 48.9 (answer from book) I just need to show how to get that

HUH! I SUCK at math

Whats your major?

you will have to get your trig book out and look under "trig identitys" for this.  I could, but I'm feelin plumb lazy.  

Quoted: Quoted: 42 close i know the answer is approx 48.9 (answer from book) I just need to show how to get that

I knew it.

Quoted: Quoted: 42 Yeah, but what's the QUESTION, wiseass?

Not sure, but it probably has something to do with Swallows.

Quoted: Whats your major? you will have to get your trig book out and look under "trig identitys" for this.  I could, but I'm feelin plumb lazy.

Im going for civil. I tried using cos(theta) = (1-(sin^2(theta))^.5

but my value for theta doesnt work in the original equation then

87

use a TI-89 calc to solve it

Quoted: use a TI-89 calc to solve it

+1 I love my 89

Quoted: Quoted: Whats your major? you will have to get your trig book out and look under "trig identitys" for this.  I could, but I'm feelin plumb lazy.   Im going for civil. I tried using cos(theta) = (1-(sin^2(theta))^.5 but my value for theta doesnt work in the original equation then

let me get back to you on that....

Pie are round  Cornbread are square!!!!!!

Hope that helps!!!


Bob

Factor out the theta.  So you get
230=(theta)(360sin - 63cos)
Then divide both sides by that "too much to type"
so you get
230/360sin - 63cos=theta

That's algebra, the cos and sin threw me off, that's calculus.  But I think that's what the answer is.

Quoted: Quoted: Quoted: 42 Yeah, but what's the QUESTION, wiseass? Not sure, but it probably has something to do with Swallows.

What do you mean? African or European swallows?

Quoted: Factor out the theta.  So you get 230=(theta)(360sin - 63cos) Then divide both sides by that "too much to type" so you get 230/360sin - 63cos=theta That's algebra, the cos and sin threw me off, that's calculus.  But I think that's what the answer is.

sin and cos are functions of theta, so ive got to keep them together

Quoted: Factor out the theta.  So you get 230=(theta)(360sin - 63cos) Then divide both sides by that "too much to type" so you get 230/360sin - 63cos=theta That's algebra, the cos and sin threw me off, that's calculus.  But I think that's what the answer is.

Just say no.  

maybe use that damn theorem.....sin squared plus cosine squared = 1?  somehow tie that in.......damn I don't have much to show for masters in mechanical engineering

After you get the math problem solved, work on your punctuation and capitalization.

well, i appreciate the effort guys

but i think im gonna just say "screw it" on this one

NOOOOO!!!!  I'm going to be thinking about this one all night now!  Must know the answer!!!!!

Then again, I took calculus like 15 years ago........
But I passed.

Quoted: well, i appreciate the effort guys but i think im gonna just say "screw it" on this one

\

NOOO !  NOOO!  You have gotten me stuck on this fucking thing!  I must find the answer!

Quoted: Quoted: well, i appreciate the effort guys but i think im gonna just say "screw it" on this one \ NOOO !  NOOO!  You have gotten me stuck on this fucking thing!  I must find the answer!

you should see how the problem started - A force P is applied to the lever of an arbor press. Knowing that P lies in a plane parallel to the yz plane, and Mx= 230 lb in, My= -200 lb in, and Mz= -35 lb in, determine the magnitude of P and the values of theta and phi.

yeah will that work? square everything and insert (1-cos theta squared) for sin squared, multiply all that out, and then take the square root of the whole shebang and take the inverse sin to get theta? I bet that's it..that damn pathagoriem thereom or something

Quoted: yeah will that work? square everything and insert (1-cos theta squared) for sin squared, multiply all that out, and then take the square root of the whole shebang and take the inverse cosine to get theta?

for some dumb reason i keep getting something that doesnt work, I must be screwing up when i simplify the radical

nah see
230^2=360^2(1-costheta^2)-63^2(costheta^2)

number=number(1-x^2)-number(x^2)

multiply out

move the x to the left it's positive and the number on the right is positive, maybe...damn

get x

take the inverse cosine of the X

Quoted: Quoted: Quoted: well, i appreciate the effort guys but i think im gonna just say "screw it" on this one \ NOOO !  NOOO!  You have gotten me stuck on this fucking thing!  I must find the answer! you should see how the problem started - A force P is applied to the lever of an arbor press. Knowing that P lies in a plane parallel to the yz plane, and Mx= 230 lb in, My= -200 lb in, and Mz= -35 lb in, determine the magnitude of P and the values of theta and phi.

I am going to say that you set the problem up wrong.  

fuck it.  

Quoted: fuck it.

i left out the picture showing where theta and phi are, so it would make more sense then

Knowing how the problem started would have been valuable info 20 minutes or so ago.  Told you it was calculus........

Instant migrane.

Quoted: Quoted: fuck it.   i left out the picture showing where theta and phi are, so it would make more sense then

Dude, VALUABLE INFO.  I'm thinking you'r math teacheer is mean throwing in sin and cos.  If you got a problem, state the WHOLE problem.  Don't leave out details!

Here is how to solve it without remembering how to do the math.

Do a trial-and-error solution.  Use a spreadsheet like exel.

But first, spread sheets like angles in radians not degrees, so you have to change the angles from degrees to radians, here is how.  (radians = degrees/360 * 2 * 3.1416).  Use a more accurate version of PI though.

Next, set up Place for a staring angle, like zero degrees and a place for increment size, like one.
That is, say, the starting degrees in A5 and the starting increment in B5.

Then build a column for the degrees that starts with the 'starting degrees' and increments with the 'increment size'.  For instance start in A10 by using =A5.  
In A11 you would have =A10+$B$5.  Copy this A11 cell down the page until it gets to 360 or 400.

Next, build a column for theta.  I would start in C10 with =(360*sin(A10/360*2*3.1416)-63*cos(A10/360*2*3.1416)).  Copy this cell down the C column, as far as the A column goes.  But, use the PI built into the machine or a more accurate PI than I used.

Look for something closest to 230 in the C column.  You will see the answer lies after 40 and before 50 degrees.

Then change the 'start degrees' to 40 and the 'increment size to 0.1.  Hmmm, we need to change the 'start degrees' to more like 48.  OK, change the increment size to 0.01.

Keep changing the 'start degrees' and 'increment size' until you "converge on a solution".  Take the A and C columns out to four places when you are almost "converged".

I got:  theta = 48.9265, giving 230.000.  But a longer version of PI would have given a slightly more accurate answer.  

In computing, this sort of trial and error solution is called a newton-raphson solution, aka numerical solution.

This "numerical solution" technique is used in engineering a lot, because only four percent of all differential equations have a math-department solution (analytical solution), but engineers still have to solve those equations.

I hope this helps.

Mike S

And now we know why London Bridge will fall down again - the sizing is screwed up and no one can read the drawings.