Question

concave mirror gives image 3 times as larrge as object placed at 20cmfrom it. calfocal length if image is real

Answer 1

as it is a concave mirror,
object distance u= -20 also image is real
m=-v/u
m=3 and u= -20
so,
3=-v/-20
thus v= -60
to find the focal length,we must use the mirror formula
1/v + 1/u =1/f
1/-60 +1/-20 =1/f
so if you calculate it,we get f= -15cm.
hope it helps!!!