Дана функция z =e^xy. показать, что x^2*((d^2z)/(dx^2))-2xy*((d^2z)/(dx dy))+y^2*((d^2z)/(dy^2))=0

at 1st september i went to school at first day of school life. it was rather funny we have little concert at school stadium. i saw a lot of little pupils from 1st grade and adult students from 11th grade. and when i compare   my 1st september 5 years ago i remember very colorful holiday it was amazing. and i will remember it for years.