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szerokośc-7 cm
Ob=30
P=a*b 56=7*8
Ob=2a+2b 2*7+2*8=30
P = 56 cm²
Obw = 30 cm
a = ? [cm]
b = ? [cm]
ab = 56
2(a + b) = 30 /:2
a + b = 15
b = 15 - a
a(15 - a) = 56
15a - a² = 56
a² - 15a + 56 = 0
Δ = 225 - 224 = 1
a = (15 - 1)/2 lub a = (15 + 1)/2
a = 7 cm lub a = 8 cm
b = 8 cm lub b = 7 cm
Odp: Boki prostokąta wynoszą: 7cm, 8cm.