1)a1=3,a2=7,a3=11,a4=15,, a23=?
d=a2-a1=a3-a2=a4-a3=, d=7-3, d=4
an=a1+(n-1)d
a23=3+22.4=3+88=91
a23=91
2)a1=-5, a2=-1,a3=3,a4=7
d=-1-(-5)=-1+5=4 , d=4
a23=-5+22.4=-5+88=83
a23=83
