| 2n+3 | ||
an = | ||
| n+1 |
| 2n+5 | ||
an+1 = | ||
| n+2 |
| 2n+5 | 2n+3 | (2n+5)(n+1) − (2n+3)(n+2) | ||||
an+1 − an = | − | = | = | |||
| n+2 | n+1 | (n+1)(n+2) |
| 2n2+7n+5−2n2−5n−6 | 2n−1 | |||
= | > 0 | |||
| (n+1)(n+2) | (n+1)(n+2) |
| 2n2 + 7n + 5 − 2n2 − 7n − 6 | ||
= | = ... | |
| (n + 1)(n + 2) |
| 2n2 + 2n+5n+5−2n2−4n−3n−6 | −1 | ||
= | <0 | ||
| (n+2)(n+1) | (n+2)(n+1) |