Найти частные производные dzdx; dzdy; d2zdx2; d2zdy2; d2zdxdy функции. z=2arctg8x+9y

Dzdx=2arctg8x+9yx'=21+8x+9y2*8x+9yx'=161+8x+9y2
dzdy=2arctg8x+9yy'=21+8x+9y2*8x+9yy'=181+8x+9y2
d2zdx2=161+8x+9y2x'=16x'1+8x+9y2-161+8x+9y2x'1+8x+9y22=0-16*28x+9y*81+8x+9y22=-2568x+9y1+8x+9y22
d2zdy2=181+8x+9y2y'=18y'1+8x+9y2-181+8x+9y2y'1+8x+9y22=0-18*28x+9y*91+8x+9y22=-3248x+9y1+8x+9y22
d2zdxdy=161+8x+9y2y'=16y'1+8x+9y2-161+8x+9y2y'1+8x+9y22=0-16*28x+9y*91+8x+9y22=-2888x+9y1+8x+9y22