tentukan jumlah dari 100 suku pertama pada deret aritmatika a.2+7+13+17+... b.6+10+14+18+... c. 50+45+40+35+... d.16+12+8+4+...

a. 2 + 7 + 13 + 17...
a = 2
b = 7 - 2 = 5
Sn = n/2 x [2a + (n-1)b]
S100 = 100/2 x ( 2(2) + (100-1)5)
S100 = 50 x (4 + 495)
S100 = 50 x 499
S100 = 24950

b. 6 + 10 + 14 + 18 + ...
a = 6
b = 10 - 6 = 4
S100 = 100/2 x (2(6) + 99(4))
S100 = 50 x ( 12 + 396)
S100 = 50 x 408
S100 = 20400

c. 50 + 45 + 40 + 35 + ...
a = 50
b = 45 - 50 = -5
S100 = 100/2 x (2(50) + 99(-5))
S100 = 50 x (100 - 495)
S100 = 50 x (-395)
S100 = -19750 = 19750

d. 16 + 12 + 8 + 4 +...
a = 16
b = 12 - 16 = -4
S100 = 100/2 x (2(16) + 99(-4))
S100 = 50 x (32 - 396)
S100 = 50 x (-364)
S100 = -18200 = 18200