pada gambar diatas jika foto dan karton sebangun, hitunglah lebar karton di bawah foto!

Pk/pf = lk / lf
50/50-7-x = 40/40-4-4
50/43-x = 40/32
50x32. = 40x43 - 40x X
1600. = 1720 - 40x
40x. = 1720 - 1600
40x. = 120
X. = 3
Jadi lebar fto bawah 3 cm

Kesebangunan
p = 40 cm
l = 50 cm
a = 4cm
b = 7

P karton/L karton = P foto/L foto
40/50 = (40-4-4)/(50-7-x)
4/5 = 32/43-x
43 - x = 5/4 (32)
43 - x = 40
x = 3 cm