Ob = 139cm
5x - 1 + 4x + 7 + 3x + 12 = 139
12x + 18 = 139
12x = 139 - 18
12x = 121 /:12
x = [tex]\frac{121}{12}[/tex]
x = [tex]10\frac{1}{12}[/tex]
1 bok: 5x - 1 = 5 × [tex]\frac{121}{12}[/tex] - 1 = [tex]\frac{605}{12}[/tex] - [tex]\frac{12}{12}[/tex] =[tex]\frac{593}{12}[/tex] = [tex]49\frac{5}{12}[/tex] (cm)
2 bok: 4x + 7 = 4 × [tex]\frac{121}{12}[/tex] + 7 = [tex]\frac{121}{3}[/tex] + [tex]\frac{21}{3}[/tex] = [tex]\frac{142}{3}[/tex]= [tex]47\frac{1}{3}[/tex] (cm)
3 bok: 3x + 12 = 3 × [tex]\frac{121}{12}[/tex] + 12 = [tex]\frac{121}{4}[/tex] + [tex]\frac{48}{4}[/tex] = [tex]\frac{169}{4}[/tex] = [tex]42\frac{1}{4}[/tex] (cm)
Gdyby obwód wynosił 138 cm
5x - 1 + 4x + 7 + 3x + 12 = 138
12x + 18 = 138
12x = 138 -18
12x = 120 /:10
x = 10
1 bok: 5x -1 = 5 × 10 - 1 = 50 - 1 = 49(cm)
2 bok: 4x + 7 = 4 × 10 + 7 = 40 + 7 = 47 (cm)
3 bok: 3x + 12 = 3 × 10 + 12 = 30 + 12 = 42 (cm)
