limit as x approaches 0 of (4x)/(tan(x))

解答

x \to 0 lim (\frac{4 x}{tan ( x )})

4

求解步骤

x \to 0 lim (\frac{4 x}{tan ( x )})

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

= 4 \cdot x \to 0 lim (\frac{x}{tan ( x )})

使用基本三角恒等式:

\frac{1}{tan ( x )} = cot (x)

= 4 \cdot x \to 0 lim (x cot (x))

改写以应用洛必达法则

= 4 \cdot x \to 0 lim (\frac{x}{\frac{1}{c o t ( x )}})

使用洛必达法则

= 4 \cdot x \to 0 lim (\frac{1}{sec ^{2} ( x )})

代入值

x = 0

= 4 \cdot \frac{1}{sec ^{2} ( 0 )}

化简

4 \cdot \frac{1}{sec ^{2} ( 0 )} : 4

= 4

\int [\frac{100}{25 + ( 5 y ) ^{2}} + e^{4}] d y

y^{^{'}} = e^{2 x} + 3 y

\int \frac{1}{x ^{2} + a ^{2}} d x

t an g e n t f (x) = 5 x - x^{2}, at x = 1

y^{^{'}} = 2 (1 + x) (1 + y^{2}), y (0) = 0