Question

NEED HELP ASAP!!!! 15POINTS!

Factor k^2 - 81.
(k + 9)(k + 9)
(k - 9)(k - 9)
(k - 9)(k + 9)

Answer 1

it’s (k-9)(k+9) because when expanded you get k^2 +9k -9k -81 which simplifies to = k^2-81. a good trick with questions like this is square root the second number which in this instance is 9 and you will have a plus bracket and a minus bracket. (k+9)(k-9)

Answer 2

(k +9)(k - 9)

Explanation:

a² - b² = (a + b)(a -b)

k² - 81 = k² - 9²

= (k +9)(k - 9)