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Answers for “为什么 $\sqrt{x}$ 在 $x=0$ 处的导数不存在?”

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The limit definition fails to produce a finite derivative for f(x)=xf(x)=\sqrt{x} at x=0x=0. While the formula yields 12x\frac{1}{2\sqrt{x}} for x>0x>0, substituting x=0x=0 results in division by zero, indicating that the slope of the tangent line is vertical and the derivative is undefined (infinite) at that point.

Conditions: f(x)=xf(x)=\sqrt{x}.; The point of evaluation is x=0x=0.; The limit is taken as h→0+h \to 0^+ (since the domain is x≥0x \ge 0).

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To find the derivative of f(x)=xf(x)=\sqrt{x}, substitute into the difference quotient x+h−xh\frac{\sqrt{x+h}-\sqrt{x}}{h}. Multiply the numerator and denominator by the conjugate x+h+x\sqrt{x+h}+\sqrt{x} to rationalize the numerator.

Conditions: f(x)=xf(x)=\sqrt{x}.; x>0x > 0 for the derivative to be finite.; hh is nonzero during the algebraic manipulation.