Respuesta :

k2 - 81 = (k + 9)(k -9)

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charlottekrist
1. Rewrite it in the form a^2-b^2, where a=k and b=9
k^2-9^2

2. Use difference of squares: a^2-b^2 = (a+b)(a-b)
(k+9)(k-9)