Ответ (Неопределённый)
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/ ___\
___ ____ |x*\/ 6 |
/ \/ 6 *\/ pi *C|-------|
| | ____|
| / 2\ \ \/ pi /
| cos\3*x / dx = C + -----------------------
| 6
/
$$-{{\sqrt{\pi}\,\left(\left(\sqrt{2}\,\sqrt{3}\,i-\sqrt{2}\,\sqrt{3}
\right)\,\mathrm{erf}\left({{\left(\sqrt{2}\,\sqrt{3}\,i+\sqrt{2}\,
\sqrt{3}\right)\,x}\over{2}}\right)+\left(\sqrt{2}\,\sqrt{3}\,i+
\sqrt{2}\,\sqrt{3}\right)\,\mathrm{erf}\left({{\left(\sqrt{2}\,
\sqrt{3}\,i-\sqrt{2}\,\sqrt{3}\right)\,x}\over{2}}\right)+\left(-
\sqrt{2}\,\sqrt{3}\,i-\sqrt{2}\,\sqrt{3}\right)\,\mathrm{erf}\left(
\sqrt{3}\,\sqrt{-i}\,x\right)+\left(\sqrt{2}\,\sqrt{3}\,i-\sqrt{2}\,
\sqrt{3}\right)\,\mathrm{erf}\left(\left(-1\right)^{{{1}\over{4}}}\,
\sqrt{3}\,x\right)\right)}\over{48}}$$
/ ___ \
___ ____ |\/ 6 |
\/ 6 *\/ pi *C|------|*Gamma(1/4)
| ____|
\\/ pi /
---------------------------------
24*Gamma(5/4)
$$-{{\sqrt{\pi}\,\left(\left(\sqrt{2}\,\sqrt{3}\,i-\sqrt{2}\,\sqrt{3}
\right)\,\mathrm{erf}\left({{\sqrt{2}\,\sqrt{3}\,i+\sqrt{2}\,\sqrt{3
}}\over{2}}\right)+\left(\sqrt{2}\,\sqrt{3}\,i+\sqrt{2}\,\sqrt{3}
\right)\,\mathrm{erf}\left({{\sqrt{2}\,\sqrt{3}\,i-\sqrt{2}\,\sqrt{3
}}\over{2}}\right)+\left(-\sqrt{2}\,\sqrt{3}\,i-\sqrt{2}\,\sqrt{3}
\right)\,\mathrm{erf}\left(\sqrt{3}\,\sqrt{-i}\right)+\left(\sqrt{2}
\,\sqrt{3}\,i-\sqrt{2}\,\sqrt{3}\right)\,\mathrm{erf}\left(\left(-1
\right)^{{{1}\over{4}}}\,\sqrt{3}\right)\right)}\over{48}}$$
=
/ ___ \
___ ____ |\/ 6 |
\/ 6 *\/ pi *C|------|*Gamma(1/4)
| ____|
\\/ pi /
---------------------------------
24*Gamma(5/4)
$$\frac{\sqrt{6} \sqrt{\pi} C\left(\frac{\sqrt{6}}{\sqrt{\pi}}\right) \Gamma\left(\frac{1}{4}\right)}{24 \Gamma\left(\frac{5}{4}\right)}$$