Exercise · ZW-PARTIAL-DERIVATIVE-005 · ★★☆ Intermediate
For \(f(x,y)=\sqrt{x^2+y^2}\), what is \(f_x(3,4)\)?
Choose one option.
Show answer
- B. \(\frac{3}{5}\)
Explanation
\(f_x=\dfrac{x}{\sqrt{x^2+y^2}}\), which equals \(\dfrac35\) at \((3,4)\).
Review the concept: Partial derivative
The partial derivative of a function \(f(x,y)\) with respect to \(x\) at a point \((a,b)\) is the ordinary derivative of the one-variable function obtained by fixing \(y=b\) and letting only \(x\) vary.
\[f_x(a,b)=\lim_{h\to0}\frac{f(a+h,b)-f(a,b)}{h}\]
More practice problems: partial derivative
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- ZW-PARTIAL-DERIVATIVE-003 Compute (∂)/(∂ x)sin (xy).
- ZW-PARTIAL-DERIVATIVE-004 If f(x,y)=e^xy^2, what is f_y(1,1)?
- ZW-PARTIAL-DERIVATIVE-006 If f(x,y)=xln y, what is f_y(2,e)?
- ZW-PARTIAL-DERIVATIVE-007 For f(x,y)=x^2y^3, compute the mixed partial derivative f_xy=(∂)/(∂ y)(f_x).
- ZW-PARTIAL-DERIVATIVE-008 The surface z=9-x^2-y^2 is cut by the plane y=2. What is the slope of the resulting curve where x=1?
- ZW-PARTIAL-DERIVATIVE-009 For f(x,y)=|x|+y, which statement is true at the origin?