Motivation behind the question: I've wondered since grade 10 that if $\sin(a+b),\sin(a-b)$ have formulas in terms of $\sin(a)$ and $\sin(b)$, then why not $\sin(ab)$. But I couldn't find any such information sadly. My attempt:- $$\sin(ab)=\sin\bigg(\frac{(a+b)^2}{4}-\frac{(a-b)^2}{4}\bigg)$$ This...
Motivation behind the question: I've wondered since grade 10 that if $\sin(a+b),\sin(a-b)$ have formulas in terms of $\sin(a)$ and $\sin(b)$, then why not $\sin(ab)$. But I couldn't find any such information sadly. My attempt:- $$\sin(ab)=\sin\bigg(\frac{(a+b)^2}{4}-\frac{(a-b)^2}{4}\bigg)$$ This...
Theorem I.5.15 of the book (Freitag&Busam complex analysis) says: A map $f:D\to D'$, where $D,D'$ open in $\mathbb{C}$, is locally conformal if and only if it is analytic and its derivative is analytic and does not vanish anywhere. At this point in the book, Cauchy integral theorem or CIF haven't...
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