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Lebar persegi panjang adalah sepertiga dari panjang nya. Jika keliling persegi panjang tersebut 56cm56\,\text{cm}. Berapakah luas persegi panjang tersebut?

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Q. Lebar persegi panjang adalah sepertiga dari panjang nya. Jika keliling persegi panjang tersebut 56cm56\,\text{cm}. Berapakah luas persegi panjang tersebut?
  1. Define Variables: Let's call the length of the rectangle LL and the width WW. We know that W=L3W = \frac{L}{3} and the perimeter P=2L+2W=56cmP = 2L + 2W = 56\,\text{cm}.
  2. Express Width in Terms of Length: First, let's express WW in terms of LL: W=L3W = \frac{L}{3}.
  3. Plug Width into Perimeter Formula: Now, let's plug WW into the perimeter formula: P=2L+2(L3)=56P = 2L + 2\left(\frac{L}{3}\right) = 56.
  4. Simplify Equation: Simplify the equation: 2L+2L3=562L + \frac{2L}{3} = 56.
  5. Multiply to Eliminate Fraction: Multiply everything by 33 to get rid of the fraction: 6L+2L=1686L + 2L = 168.
  6. Combine Like Terms: Combine like terms: 8L=1688L = 168.
  7. Find Length: Divide both sides by 88 to find LL: L=1688=21L = \frac{168}{8} = 21 cm.
  8. Find Width: Now we can find WW using W=L3W = \frac{L}{3}: W=213=7W = \frac{21}{3} = 7 cm.
  9. Calculate Area: Finally, calculate the area AA of the rectangle using A=L×WA = L \times W: A=21×7=147 cm2A = 21 \times 7 = 147 \text{ cm}^2.

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