@@ End of Day Wrap Sun 22/2/15 Sydney, Australia Time 1:15 am (Really mon morning) ♪ ♫
Hi everyone,
Great answers today from ChaosBolt, CPhill, Lizzylizard7, Tetration, alan, Rosala, Mathematician, Heureka and SevenUp. Thanks all.
Interest Posts:
1) Using Venn diagrams. Thanks CPhill
2) Probability - A problem with permutations. LOL Thanks CPhill.
3) Senior Trigonometry - (But not too hard) Thanks Melody and CPhill
4) Phi function. Thanks Heureka
5) Can a line be straight when the Earth is a sphere? I've answered but I'd like others to answer too.
6) Physics - basic energy question. Thanks anon
7) Excellent calculus question. Melody
8) Finding all the 5th roots of a complex number. Melody
9) Integration with trig. (If I find time I really want to do this one) Thanks Alan.
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Mon 23/2/15
1) A suggestion for casual answerers An old one that has had attention drawn back to it.
2) Vectors Thanks CPhill
3) Complex numbers (maybe) Melody
4) phi(6) Yes again, LOL Thanks Heureka
5) Arithmetic Progression. Thanks CPhill
6) Nasty looking function question. Thanks Alan
7) Tricky Calculus Thanks CPhill and Melody
8) Number puzzle, Thanks anon and Chris.
9) Physics, Electical charges. Thanks SevenUp and Alan
♫♪ ♪ ♫ ♬ ♬ MELODY ♬ ♬ ♫♪ ♪ ♫
$$\sqrt[5]{8-15i}$$
I saw Alan do one like this recently. I will give it a go.
$$\sqrt{8^2+15^2}=17$$
$$\\8-15i = 17\left(\frac{8}{17}-\frac{15}{17}i\right)=17(cos\theta+isin\theta)=17e^{i\theta}\\\\
cos\theta=\frac{8}{17}\\
sin\theta=-\frac{15}{17}\\
\theta $ must be in the 4th quad $\\
tan\theta=-\frac{15}{8}\\
\theta\approx -61.9275\\\\
\sqrt[5]{8-15i}\\
=(17e^{i\theta})^{1/5}\\
=17^{1/5}e^{(\theta/5)i}\\
=17^{1/5}e^{(-61.9275/5)i}\\
=17^{1/5}e^{(-61.9275/5)i}\\
=1.7623e^{-12.3855i}\\$$
now these angles are in degrees abd 360/5=72degrees
-12.3855+72=59.61
59.61+72=131.61
131.61+72=203.61
203.61+72=275.61
275.61+72=347.61
so the radius of the polar co-ordinates is 1.7623 and $$\theta$$ = 59.61, 131.61, 203.61, 275.61 and 347.61
these polar co-ordinates are graphed on this page
http://www.wolframalpha.com/input/?s=51&_=1424610503524&i=%288-15i%29^%281%2f5%29&fp=1&incTime=true
Now I suppose I should change these polar coordinates back to standard complex numbers but it is very late for me and it is all a bit much for now.
That should be a good start for you anyway.