-4,-2,0,2,4,....... Tentukan Rumus Suku ke N dan jumlah 20 suku pertama

b = -2 -(-4) = 2
Un = -4 + (n-1)2

S20 = 20/2 [2(-4) + (19)2]
=> 10 ( -8 + 38)
=> 10 (30)
=> 300

A = -4
B = -2 - (-4) = 2

Un :
= a + (n-1) x b
= -4 + (n-1) x 2
= -4 + 2n -2
= -6 + 2n

S20 :
= n/2 x [2a + (n-1) x b]
= 20/2 x [2 x -4 + (20-1) x 2]
= 10 x [-8 + 19 x 2]
= 10 x [-8 + 38]
= 10 x 30
= 300