What adds to 1 and multiples to - 90

+10 and - 9

Step-by-step explanation:

If we consider the multiples of - 90

± 1, ± 2, ± 3, ± 5, ± 6, ± 9, ± 10, ± 15, ± 30, ± 90

The combination of multiples which multiply to - 90 and add to + 1 are

+ 10 and - 9

since 10 * - 9 = - 90 and 10 - 9 = 1