my 3 c

<img src="http://img.blog.csdn.net/20160923175403386" alt="" />#include <stdio.h>#include <stdlib.h>int main(){    float r1,r2,r;    scanf("%f %f",&r1,&r2);    r=1/(1/r1+1/r2);    printf("1/(1/%f+1/%f)=%f\n",r1,r2,r);    return 0;}