Question

plz plz help me plz plz plz plz plz plz plz!

Answer 1

12)n/2[2a+(n-1)d]
10[2+19(3)]=590

Answer 2

11) a5 + a6= 74
a+4d+a+5d=74
2a+9d=74 -----(1)

a4+a2=44
a+3d+a+d=44
2a+4d=44----(2)
subtracting (1) and (2)
5d=30
d=6
putting d=6 in equation (2)
2a+4*6=44
2a+24=44
2a=20
a=10 (therefore AP is 10,16,22....)

12) a=1,n=20,d=3
Sn=n/2[2a+(n-1)d]
=20/2[2*1+(20-1)3]
=10[2+19*3]
=10[2+57]
=10*59
590