text: Function to find the length of the direct common tangent
code: void lengtang ( double r1 , double r2 , double d ) { cout << " The ▁ length ▁ of ▁ the ▁ direct " << " ▁ common ▁ tangent ▁ is ▁ " << sqrt ( pow ( d , 2 ) - pow ( ( r1 - r2 ) , 2 ) ) << endl ; }