Question

Tolong dijawab ya PR buat besok nih penting!

Balok berukuran panjang (2x + 6)cm, lebar (2x - 2)cm, tinggi (3x + 4)cm. sedangkan jumlah panjang rusuk-rusuknya 228 cm. Berapa luas permukaan balok tersebut?
*jawabnya pake rumus ya.
mohon bantuannya :-)

Answer 1

Jumlah panjang rusuk = (4 x p) + (4 x l) + (4 x t)
228 = (4 x (2x+6) ) + (4 x (2x-2)) + (4 x (3x+4))
228 = (8x + 24) + (8x - 8) + (12x + 16 )
228 = 8x + 24 + 8x - 8 + 12x + 16
228 -24 +8 - 16 = 8x + 8x +12x
196 = 28x
x = 196 / 28 = 7

p = 2 (7) + 6 = 20
l = 2 (7) -2 = 12
t = 3 (7) +4 = 25

luas permukaan = 2 (p x l) + 2 (p x t) + 2 (l x t)
= 2 (20 x 12) + 2 (20 x 25) + 2 (12 x 25)
= 2 (240) + 2 (500) + 2 (300)
= 480 + 1000 + 600
= 2080

Answer 2

Rumus keliling = 4 x (p + l + t)

228 = 4 x ((2x+6) + (2x-2) + (3x+4))
228 = 4 x (7x + 8)
228 = 28x + 32
196 = 28x
7    = x

p = 2x + 6
   = 2.7 + 6
   = 14 + 6
   = 20 cm

l = 2x - 2
  = 2.7 - 2
  = 14 - 2
  = 12 cm

t = 3x + 4
  = 3.7 + 4
  = 25 cm

========================================================

Rumus luas permukaan=

Lp = 2 x (PL + PT + LT)
     = 2 x ((20)(12) + (20)(25) + (12)(25))
     = 2 x (240 + 500 + 300)
     = 2 x (1040)
     = 2080 cm²