
2 Attachment(s)
Sin Problem
Hello everyone,
I'm having some trouble solving this equation.
Attachment 23826
All help would be appreciated :), Thanks!
This is my work that I've done so far...
Attachment 23827
PS I know this might not be the right section for a statics problem, but I'm really only having trouble with the trig part so yeah... lol:)

Re: Sin Problem
When I plugged back in my 58.91 degrees, I should have gotten 0, but I get something like 82.8 :( not 0.

Re: Sin Problem
a)
$\displaystyle \begin{cases}90+70\cdot \sin \alpha130 \cdot \cos \alpha=0 \\\sin^2 \alpha + \cos^2 \alpha=1 \end{cases}$

Re: Sin Problem
how do you enter this cos alpha and other maths symbols in this text pad?

Re: Sin Problem
princeps, I tried that already (if you look in the picture of the work I showed), and when I solved for alpha I got 58.91 degrees. However, upon plugging it back into the problem I don't get 0.

Re: Sin Problem
starting where $\displaystyle \sum F_y = 0$ , 4th line ... one "egregious" algebra error.
note $\displaystyle (ab)^2 \ne a^2 + b^2$

Re: Sin Problem
Ahhhh I see. Thank you :)!

Re: Sin Problem
$\displaystyle a\cos{x}  b\sin{x} = R\cos(x+t)$
$\displaystyle R = \sqrt{a^2+b^2}$ , $\displaystyle \tan{t} = \frac{b}{a}$
let x = your "$\displaystyle \alpha$" ...
$\displaystyle 13\cos{x}  7\sin{x} = 9$
$\displaystyle R = \sqrt{13^2 + 7^2}$ , $\displaystyle t = \arctan\left(\frac{7}{13}\right)$
$\displaystyle R \cos(x + t) = 9$
$\displaystyle x+t = \arccos\left(\frac{9}{R}\right)$
$\displaystyle x = \arccos\left(\frac{9}{R}\right)  \arctan\left(\frac{7}{13}\right) \approx 24.14^\circ$