sin(3*x)-cos(3*x)*1/sin(3*x)+cos(3*x)

$$sin{left (3 x right )} – frac{cos{left (3 x right )}}{sin{left (3 x right )}} + cos{left (3 x right )} < 0$$

/ / ________________________________________________________________________________________________________________________
| | / ______________ ||
| | / / _____ ||
| | / 10 / 35 / 129 10 8 ||
| | / – — – 2*3 / — + ——- + ————————————————————— – ——————— ||
| | / 3 / 27 9 _____________________________________________________ ______________ _____________________________________________________||
| | / / ______________ / _____ / ______________ ||
| | / / / _____ / 35 / 129 / / _____ ||
| | / / 5 / 35 / 129 8 9*3 / — + ——- / 5 / 35 / 129 8 ||
| | / / – – + 2*3 / — + ——- + ——————— / 27 9 / – – + 2*3 / — + ——- + ——————— ||
| | / / 3 / 27 9 ______________ / 3 / 27 9 ______________ ||
| | / / / _____ / / _____ ||
| | / / / 35 / 129 / / 35 / 129 ||
| | / / 9*3 / — + ——- / 9*3 / — + ——- ||
| |1 / / / 27 9 / / 27 9 ||
| 2*atan|- + ————————————————————————————————————————————— – —————————————————————||
| 2 2 2 /|
And|0 < x, x < ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| 3 /

$$0 < x wedge x < frac{2}{3} {atan}{left (- frac{1}{2} sqrt{- frac{5}{3} + frac{8}{9 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + 2 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + frac{1}{2} sqrt{- frac{10}{3} - 2 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}} - frac{8}{9 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + frac{10}{sqrt{- frac{5}{3} + frac{8}{9 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + 2 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}}}} + frac{1}{2} right )}$$

/ ________________________________________________________________________________________________________________________
| / ______________ |
| / / _____ |
| / 10 / 35 / 129 10 8 |
| / – — – 2*3 / — + ——- + ————————————————————— – ——————— |
| / 3 / 27 9 _____________________________________________________ ______________ _____________________________________________________|
| / / ______________ / _____ / ______________ |
| / / / _____ / 35 / 129 / / _____ |
| / / 5 / 35 / 129 8 9*3 / — + ——- / 5 / 35 / 129 8 |
| / / – – + 2*3 / — + ——- + ——————— / 27 9 / – – + 2*3 / — + ——- + ——————— |
| / / 3 / 27 9 ______________ / 3 / 27 9 ______________ |
| / / / _____ / / _____ |
| / / / 35 / 129 / / 35 / 129 |
| / / 9*3 / — + ——- / 9*3 / — + ——- |
|1 / / / 27 9 / / 27 9 |
2*atan|- + ————————————————————————————————————————————— – —————————————————————|
2 2 2 /
(0, ———————————————————————————————————————————————————————————————————————)
3

$$x in left(0, frac{2}{3} {atan}{left (- frac{1}{2} sqrt{- frac{5}{3} + frac{8}{9 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + 2 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + frac{1}{2} sqrt{- frac{10}{3} – 2 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}} – frac{8}{9 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + frac{10}{sqrt{- frac{5}{3} + frac{8}{9 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}} + 2 sqrt[3]{frac{sqrt{129}}{9} + frac{35}{27}}}}} + frac{1}{2} right )}right)$$