Cho hàm số f(x, y)= a/ tính vi phân cấp 1 của hàm số tại (1,1)
b/ tính các đạo hàm riêng cấp 2 của hàm số tại (1,1)
c/ chứng minh rằng không tồn tại lim(x, y)->(0,0) f(x, y)
giúp mình nha

International calls require the use of a country code. many country codes a 3-digit numbers. country codes do not begin with a 0 or 1. there are no restrictions on the second and third digits. how many different 3-digit country codes are possible?

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling

Which is greater, 7 p 5 or 7 c 5? 7p5 7c5