Odpowiedź:
Obw=139 cm
Obw=a+b+c
a=4x+7
b=5x-1
c=3x+12
4x+7+5x-1+3x+12=139
4x+5x+3x=139-7+1-12
12x=121 |:12
x=10 1/12
a=4x+7= 10 1/12•4+7=40 4/12+7= 47 4/12= 47 ⅓ cm
b=5x-1= 10 1/12•5-1= 50 5/12-1= 49 5/12 cm
c=3x+12= 10 1/12•3+12= 30 3/12+12= 42 3/12= 42 ¼ cm
