Question

how we will know that when is image formation is positive or negative
also by tell how image is denoted by v or u​

Answer 1

if image is behind mirror it's positive and if it's in front of mirror means it's in side of object ..then it's negative...

in lens...

means if it's other side of object then positive and same side of object it's negative

Answer 2

if the image is on left hand then we will take image as -ve ,and if the image is on right hand side the we will take image as +ve