Find the least common denominator for these two rational expressions

a / a^2 - 6a + 9

7 / a^2 - 8a + 15

factor the 2 denominators:-

a^2 - 6a + 9 = (a - 3) (a - 3)

a^2 - 8a + 15 = (a - 3) (a - 5)

((a - 3) is common to both sets of factors so the LCD is:-

(a - 3) (a - 3) (a - 5) or this can be written as (a - 3) ^2 (a - 5)