I just have a doubt please reply my question is while finding envelope of a curve why should we differentiate the equation partially with respect to the parameter and equate it to 0 if anybody knows please clear my doubt

• i am not fully confident but what I understood is..,
  first we have to understood what is exactly envelope then it will be clear...
  let F(x,y,p)defines a function of a curve,
  let for different value of 'p' we get curves Cp. The group/family of this curve Cp forms an additional curve, making a boundary of the region swept out by the curves Cp.This curve, which is tangent at each point to the curves Cp is called envelope (E).
  that's why we partially differentiate with respect to parameter(here 'p') and equates to zero because, the curves Cp are tangential to E. so here we are to find the equation which is tangential to all curves Cp.
• 11 years agoHelpfull: Yes(0) No(0)