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1dm = 10 cm
Pole kwadratu = x²
Pole prostokąta = (x+3)×(x-10)=x²-10x+3x-30=x²-7x-30
x²=x²-7x-30+170 /-x²
0=-7x+140 /+7x
7x=140 /÷7
x=20
no i teraz jest już wszystko jasne:
ob=2×(20+3)+2×(20-10)=46+20=66cm