How to solve cos (50° + 2α) = -1

Need for my math class

cos(50 + 2a) = -1
cos(50 + 2a) = cos(180 + 360 * k)
50 + 2a = 180 + 360 * k
2a = 130 + 360 * k
a = 65 + 180 * k

k is an integer

a = 65 , 245 , 425 , 605 , .....

α=65