pada gambar diatas,PQ//BC.panjngBCadalah...

AQ ÷ AC = AP ÷ AB
12 ÷ (12 + 16) = x ÷ (x + x + 5)
12 ÷ 28 = x ÷ (2x + 5)
12 (2x + 5) = 28x
24x + 60 = 28x
28x - 24x = 60
4x = 60
x = 15 cm

PB = x + 5 = 15 + 5 = 20 cm

[tex] \frac{AC}{AB} = \frac{AQ}{AP} [/tex]
[tex] \frac{12 + 16}{x + (x + 5)} = \frac{12}{x} [/tex]
[tex] \frac{28}{2x + 5} = \frac{12}{x} [/tex]
28x = 12(2x+5)
28x = 24x + 60
  4x = 60
    x = 15

PB = x + 5
      = 15 + 5
      = 20