z = 2 cis 7π/8

z = 2 (cos 7π/8 + i sin 7π/8)

　cos²(7π/8)

　= 1/2 (1 + cos 7π/4)

　= 1/2 (1 + √2/2)

　= (2+√2)/4

　cos(7π/8) = −√(2+√2)/2

　sin²(7π/8)

　= 1/2 (1 − cos 7π/4)

　= 1/2 (1 − √2/2)

　= (2−√2)/4

　sin(7π/8) = √(2−√2)/2

z = 2 (−√(2+√2)/2 + i √(2−√2)/2)

z = −√(2+√2) + i √(2−√2)

If it were to be π/6 then :-

z = 2 /_ 7π/6

z = 2 [ cos 7π/6 + j sin 7π/6 ]

z = 2 [ - √3 /2 - j (1/2) ]

z = - √3 - j

x = r cos(theta)

y = r sin(theta)