There is a discontinuity at 0 since you can’t divide cos x by 0. So that would be represented in interval notation at (-infinity, 0) U (0, infinity) replace infinity with the symbol
Ok the answer of 6 are 12, 18, 24, 30, 36, 42, and 48. The multiples of 9 are 18,27,36,45,54,63,72,81,90,99,108,117,126,135,144,153,162,171,180,189,198,. Hope it helps!