Question

D= lim \(\dfrac{6-9^{n+2}}{3+3^n+39^{n+1}}\)

Answer 1

Đề là \(39^{n+1}\) hay \(3.9^{n+1}\) vậy bạn?

Answer 2

\(=\lim\dfrac{6-9^2.9^n}{3+3^n+39.39^n}=\lim\dfrac{6-81.9^n}{3+3^n+39.39^n}\)

\(=\lim\dfrac{6.\left(\dfrac{1}{39}\right)^n-81.\left(\dfrac{9}{39}\right)^n}{3.\left(\dfrac{1}{39}\right)^n+\left(\dfrac{3}{39}\right)^n+39}=\dfrac{6.0-81.0}{3.0+0+39}=\dfrac{0}{30}=0\)