Question

Keliling suatu persegi panjang 28 cm. Jika panjangnya adalah (3x + 1) dan (x + 4) cm, luas persegi tersebut adalah...

Answer 1

K = 2(p+l)
28 = 2((3x+1)+(x+4))
28 = 2(3x+1+x+4)
28 = 2(4x+5)
28 = 8x+10
28-10=8x
18 = 8x
x = 18:8
x = 2,25

p = 3x+1 = 3x2,25+1 = 7,75 cm
l = x+4 = 2,25+4 = 6,25 cm

L= p x l
L = 7,75 x 6,25 = 48,4375 cm²

Answer 2

Keliling = 2.(p + l)
      28  = 2 ( 3x + 1 + x + 4)
       14 = 4x + 5
       4x = 14 - 5
       4x = 9
         x = 9/4 cm
p = 3x + 1
   = 3.(9/4) + 1
   = (27/4) + 1
   = 31/4 cm
   = 7 3/4 m
l = x + 4
  = (9/4) + 4
  = 25/4 cm
  = 6 1/4 cm
L = p x l
   = 31/4 x 25/4
   = 775/16 cm²
   = 48 7/16 cm²