if xy > 0 , 1 / x + 1 / y = 2 , and 1 / xy = 8 , then ( x + y ) / 4 = ?
"( 1 / x + 1 / y ) = 2 canbe solved as { ( x + y ) / xy } = 8 . substituting for 1 / xy = 8 , we get x + y = 2 / 8 = = > ( x + y ) / 4 = 2 / ( 8 * 4 ) = 1 / 16 . a"
divide(divide(2, 8), 8)