jika jumlah suku ke2 dan ke8 sebesar 40 dan jumlah suku ke3 dan ke6 sebesar 36. hitunglah s1, s5, dan j5 tolong jawab yaa..

u2 + u 8 = 40
u3 + u6 = 36

a+b+a+7b = 40
2a+8b = 40 ......(i)


a+2b+a+5b = 36
2a+7b = 36 .....(ii)


2a+8b = 40
2a+7b = 36
---------------- -
b = 4

2a+7b =36
2a+7(4) = 36
2a + 28 = 36
2a = 36 - 28
2a = 8
a = 4

u1 = a
u5 = a+(n-1)b
= a+4b
= 4 + 4(4)
= 4+16 =20


s5 = n/2(a+un)
= n/2(a+u5)
= 5/2(4+20)
= 5/2 . 24
= 5 . 12
= 60