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#include <iostream>using namespace std;class myrunge{   public:   virtual double fk(double x);};double myrunge::fk(double x){   return (a * x);}class RungeKutta : public myrunge{      public:      void step(double *pt, double *px, double h);      double fk(double x);      private w;};void RungeKutta::step(double *pt, double *px, double h){   double f;   *px = 1 + h * fk(0,1);   *px = 1 + (h / 2) * ( fk(0,1) + fk(*pt,*px));    f = fk(*pt,*px);   *pt = *pt + 0.1;}int main(){    return 0;}