d=a2-a1=5-2=3
a1=2
a14=a1+13d=2+13*3=2+39=41
a14=2+3(14-1)
a14=41
a20=2+3(20-1)
a20=59
S20=(2+59)20*1/2=610
d=a2-a1=5-2=3
a1=2
a14=a1+13d=2+13*3=2+39=41
a14=2+3(14-1)
a14=41
a20=2+3(20-1)
a20=59
S20=(2+59)20*1/2=610