Function to find the length of the direct common tangent
static void lengtang ( double r1 , double r2 , double d ) { System . out . println ( " The ▁ length ▁ of ▁ the ▁ direct " + " ▁ common ▁ tangent ▁ is ▁ " + ( Math . sqrt ( Math . pow ( d , 2 ) - Math . pow ( ( r1 - r2 ) , 2 ) ) ) ) ; }