n = 20
d = 6
a = 4
L = a + (n - 1)*d
L = 4 + (20 - 1)*6
L = 4 + 19*6
L = 118
Sum = (a + L)*n/2
Sum = (4 + 118) * 20/2
Sum = 122 * 10
Sum = 1220
Answer:
The coordinates of 8i on the a complex plane are
(0, 8i)
12 + z = 15
12 - 12 + z = 15 - 12
0 + z = 3
z = 3
