Найти частные производные. z=cos(x-√xy³) ​

Du/dx=3x²y³(tg²(x³y³)+1)
d²u/dx²=6xy³(tg²(x³y³)+1)+3x²y³2(tg(x³y³)3x²y³(tg²(x³y³)+1)==6xy³(3x³y³tg(x³y³)+1)(tg²(x³y³)+1)
Аналогично 
du/dy=3x3y2(tg²(x³y³)+1)
d²u/dy²=6x³y(tg²(x³y³)+1)+3x³y²2(tg(x³y³)3x³y²(tg²(x³y³)+1)==6x³y²(3x³y³tg(x³y³)+1)(tg²(x³y³)+1)
смешанные
d²u/dxdy=d(3x²y³(tg²(x³y³)+1))/dy=9x²y²(tg²(x³y³)+1)+3x²y³2tg(x³y³)3x³y²(tg²(x³y³)+1)=9x²y²(2x³y³tg(x³y³)+1)(tg²(x³y³)+1)
d²u/dydx=d(3x³y²(tg²(x³y³)+1))/dx=9x²y²(tg²(x³y³)+1)+3x³y²2tg(x³y³)3x²y³(tg²(x³y³)+1)=9x²y²(2x³y³tg(x³y³)+1)(tg²(x³y³)+1),

т.е. смешанные производные равны

285×3-408+254: 21) 253×3 = 759×25337592) 254: 2 = 127- 254 | 2 254 __ 127 03) 759-408 = 351-7594083514) 351+127 = 478+351125478ответ: 478159×5-241×3+37×91) 159×5 = 795×15957952) 241×3 = 723×24137233) 37×9 = 333×3793334) 795-723= 72-795723725) 72+333 = 405+33372405ответ: 405800-294: 3+196: 71) 294: 3 = 98-294 | 3294 __ 98 02) 196: 7 = 28-196 | 7196 __ 28 03) 800-98 = 702-800987024) 702+28 = 730+70228730ответ: 730325×3-324: 9×61) 325×3 = 975×32539752) 324: 9 = 36-324 | 9324 __ 36 03) 36×6= 216×3662164) 975-216 = 759-975216759ответ: 759