Respostas

2014-07-21T20:06:30-03:00

a4=a1+3r        a9= a1 +8r                a1= 24 -3.11           agora é só montar a PA

24=a1 +3r        79= 24- 3r +8r          a1= 24 -33

a1= 24 -3r          5r= 24-79                a1= - 9      

                            r=55/5                   

                            r= 11