Luas suatu persegi panjang 48 cm² jika panjang (x+3)cm dan lebar (2x-4)cm. Maka panjang diagonal persegi panjang adalah

L= p × l
(x + 3)(2x - 4) = 48
2x² + 2x - 12 = 48
2x² + 2x - 12 - 48 = 0
2x² + 2x - 60 = 
x² + x - 30 = 0
(x + 6) (x - 5) = 0
x - 5 = 0
     x = 5

p = x + 3
  = 5 + 3 = 8 cm
l = 2x - 4
  = 2(5) - 4 = 6 cm

d = √p² + l²
    =√ 8² + 6²
     = √64 + 36
     = √100
      = 10 cm

dik : L = 48 cm^2
p = (x+3)cm
lebar = (2x-4)cm
dit : panjang diagonal
jawab :
L = pjg × lebar
48 = (x+3)(2x-4)
48 = 2x^2 -4x + 6x -12
0 = 2x^2 +2x -60
0 = x^2 + x -30
0 = (x+6)(x-5)

x+6 =
x1 = -6 (Tidak mungkin)

x-5 = 0
x2 = 5

panjang = x+3
panjang = 5+3 = 8 cm

lebar = 2x -4
lebar = 2(5)-4 = 6 cm

diagonal = √pjg^2+lebar^2
diagonal = √8^2+6^2
diagonal = √64+36
diagonal = √100
diagonal = 10 cm