500, 410, 320

Question

To get the next term in the sequence, subtract 90 from the term before. 500 410 320 … Write the first two terms of the sequence that are less than zero.

Answer 1

The sequence is 500-90(n-1) for the nth term.

When 500-90(n-1)<0 we have a negative term.

500<90(n-1), 500<90n-90, 90n>590, n>590/90, n>59/9, n>6.56, so n≥7.

When we put n=7, we get 500-540=-40 followed by -130 as the 7th and 8th terms.