limit as x approaches 0+of 4(csc(x)-1/x)

解答

x \to 0 + lim (4 (csc (x) - \frac{1}{x}))

0

求解步骤

x \to 0 + lim (4 (csc (x) - \frac{1}{x}))

x \to a lim [c \cdot f (x)] = c \cdot x \to a lim f (x)

= 4 \cdot x \to 0 + lim (csc (x) - \frac{1}{x})

用 sin, cos 表示

= 4 \cdot x \to 0 + lim (\frac{1}{sin ( x )} - \frac{1}{x})

化简

\frac{1}{sin ( x )} - \frac{1}{x} : \frac{x - sin ( x )}{x sin ( x )}

= 4 \cdot x \to 0 + lim (\frac{x - sin ( x )}{x sin ( x )})

使用洛必达法则

= 4 \cdot x \to 0 + lim (\frac{1 - cos ( x )}{sin ( x ) + x cos ( x )})

使用洛必达法则

= 4 \cdot x \to 0 + lim (\frac{sin ( x )}{2 cos ( x ) - x sin ( x )})

代入值

x = 0

= 4 \cdot \frac{sin ( 0 )}{2 cos ( 0 ) - 0 \cdot sin ( 0 )}

化简

4 \cdot \frac{sin ( 0 )}{2 cos ( 0 ) - 0 \cdot sin ( 0 )} : 0

= 0

x \to 0 lim (\frac{arccos ( x )}{x})

x \to 3 + lim (\frac{3 x - 10}{3 - x})

x \to - \infty lim (- 7 x - 1)

x \to 1 lim (\frac{x - ∣ x ∣}{2 x})

x \to 3 lim (x^{- 1})