limit as x approaches 9 of ((x^2-4x-45))/(x^2-81)

解答

x \to 9 lim (\frac{( x ^{2} - 4 x - 45 )}{x ^{2} - 81})

\frac{7}{9}

十进制

0.77777 \dots

求解步骤

x \to 9 lim (\frac{x ^{2} - 4 x - 45}{x ^{2} - 81})

化简

\frac{x ^{2} - 4 x - 45}{x ^{2} - 81} : \frac{x + 5}{x + 9}

= x \to 9 lim (\frac{x + 5}{x + 9})

代入值

x = 9

= \frac{9 + 5}{9 + 9}

化简

\frac{9 + 5}{9 + 9} : \frac{7}{9}

= \frac{7}{9}