Classify the following partial differential equations

Classify the following partial differential equations
(i) 𝑢_𝑥𝑥 + 4𝑢_𝑥𝑦 + 4𝑢_𝑦𝑦 − 𝑢_𝑥 + 2𝑢_𝑦 = 0
(ii) 𝑥²𝑢_𝑥𝑥 + (1 − 𝑦²)𝑢_𝑦𝑦 = 0 ,−1 < 𝑦 < 1
(iii) (1 + 𝑥²)𝑢_𝑥𝑥 + (5 + 2𝑥²)𝑢_𝑥𝑡 + (4 + 𝑥²)𝑢_𝑡𝑡 = 0
(iv) 𝑦²𝑢_𝑥𝑥 − 2𝑦𝑢_𝑥𝑦 + 𝑢_𝑦𝑦 − 𝑢_𝑦 = 8𝑦

Answer:-