How do you use the definition of a derivative to find the derivative of #f(x)=8x#? Precalculus Limits, Motion, and the Tangent Line The Derivative by Definition 1 Answer sjc Dec 28, 2016 definition of derivative #(dy)/(dx)=Lim_(hrarr0)(f(x+h)-f(x))/h# Explanation: for #" "f(x)=8x# #(dy)/(dx)=Lim_(hrarr0)((8(x+h)-8x))/h# #(dy)/(dx)=Lim_(hrarr0)((cancel(8x)+8hcancel(-8x)))/h# #(dy)/(dx)=Lim_(hrarr0)(8cancel(h))/cancel(h# #(dy)/(dx)=Lim_(hrarr0)(8)=8# Answer link Related questions How do I find the derivative of a function at a given point? How do I find the derivative of a fraction? How do derivatives apply to real life? How do derivatives relate to limits? How does a partial derivative differ from an ordinary derivative? How does calculus differ from algebra? How does calculus relate to biology? What is the derivative of #e^x#? What is the derivative of #x#? What is the point of calculus? See all questions in The Derivative by Definition Impact of this question 3518 views around the world You can reuse this answer Creative Commons License