3. Tentukam jumlah deret aritmatika berikut hingga 15 suku! a. 2+4+6+... e. 5+3½+2+...

diketahui :
#b = (Un - u1)/(n - 1)

a) 2 + 4 + 6...
u15 = u1 + (n-1).b
u15 = 2 + (15 - 1). 2
u15 = 2 + 28
u15 = 30

Sn = n/2 (u1 + Un)
S15 = 15/2 (2 + 30)
S15 = 15/2 x 32
S15 = 240

e) 5 + 3 1/2 + 2
Un = u1 + (n-1).b
u15 = 5 + (15 - 1). -3/2
u15 = 5 + (-21)
u15 = -16

Sn = n/2 (u1 + Un)
S15 = 15/2 (5 + (-16))
S15 = 15/2 x (-11)
S15 = 8,25
S15 = 8 1/4

maaf klo salah