Melody

I think our answers are probably the same Heureka   

Yes Alan is right.  Drawing graphs and understanding their relevance is very useful !

Thanks Alan.  

Both answers are the same but why did you multiply by 12/12 Titanium.  That was a bit pointless  

Thaks you Chris and Fiora :))

$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}^{\!\!\mathtt{-1}}{\left({\mathtt{0.6}}\right)} = {\mathtt{36.869\: \!897\: \!645\: \!844^{\circ}}}$$

$$\\3x=180+37, \;\; 360-37,.....\\\\
x=60+(37/3), \;\; 120-(37/3), .....\\\\
x=60n+(-1)^{(n+1)}(37/3)\qquad n\in Z\\\\
x=60n+(-1)^{(n+1)}(12)\qquad n\in Z \qquad $to the closest degrees$$$

Here is a graphical solution   

Welcome to the forum BunnyBoo  :))

$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}^{\!\!\mathtt{-1}}{\left({\frac{{\mathtt{10}}}{{\mathtt{15}}}}\right)} = {\mathtt{48.189\: \!685\: \!104\: \!221^{\circ}}}$$

$$\\-2^2 = -1*2^2=-1*4=-4\\\\
whereas\\\\
(-2)^2=-2*-2=+4$$

Because it is too big a number for the calc to handle - but you are correct, it is not really  infinity.  

$$\\(X^{-2} +X^{-1})\div(X+X^{-3})\\\\
=(\frac{1}{X^{2}} +\frac{1}{X^{1}})\div(X+\frac{1}{X^{3}})\\\\
=\frac{1+X}{X^{2}} \div\frac{X^4+1}{X^{3}}\\\\
=\frac{1+X}{X^{2}} \times \frac{X^{3}}{X^4+1}\\\\
=\frac{1+X}{1} \times \frac{X}{X^4+1}\\\\
= \frac{X(X+1)}{X^4+1}\\\\$$