Mau tanya Nomer 1 Sampai 3 Beserta Cara ny ^^

1. 1/s + 1/s' = 1/f
1/4 + 1/s' = 1/8
1/s' = 1/8 - 1/4
1/s' = -1/8
s' = -8 cm (8 cm di belakang cermin)

2. 1/s + 1/s' = 1/f
1/2 + 1/s' = 1/10
1/s' = 1/10 - 1/2
1/s' = -4/10
s' = -2,5 cm (2,5 cm di belakang cermin)

3. 1/s + 1/s' = 1/f
1/2 + 1/s' = 1/5
1/s' = 1/5 - 1/2
1/s' = -3/10
s' = -10/3 cm (10/3 cm di belakang cermin)

no.2 

s = 2 cm
F = 10 cm
jawab : 1/s = 1/f + 1/s'
            1/2 = 1/10 + 1/s'
            
           1/s' = 1/2 - 1/10 =
            1/s' = 4/10
             s' = 10/4 = 2,5 
coba cek lagi barang kali ada yang salah ;)
semoga membantu