no 17 sampai 20 tolong yah,sama caranya

17) 1, 4, 9 =.> 1^2, 2^2, 3^2 , 4^2
4^2 = 16
19) 8 C 0 + 8 C 1 + 8 C 2 + 8 C 3 + 8 C 4 + 8 C 5 + 8 C 6 + 8 C 7 + 8 C 8
= 1 + 8 +28+ 66+70+66+28+8+1
=... silahkan cari
18) 1, 3, 6, 10, 15, 21, 28. adalah 28
20)Un = 2n^2-5
U1 = a = 2(1)^2-5 = -3
U2 = a + b = 2(2)^2-5= 3
a+b = 3
-3 + b = 3
b = 6
U4 + U5 = (a+3b) +(a+4b)
= 2a + 7b
= 2.(-3) + 7.6
= -6 +42
= 36