Question

the focal length of a concave mirroris 30 cm. find the position of the object in front of the mirror so that the image is three times the size of the object​

Answer 1

f is -ve. -4/3u = 1/(-30) => u = 40 cm that is 40 cm infront of the mirror. -2/3 u = -1/30 u = 20 cm that is 20 cm in front of mirror.