if a - b = 3 and a ( power 2 ) + b ( power 2 ) = 21 , find the value of ab .
"2 ab = ( a ( power 2 ) + b ( power 2 ) - ( a - b ) ( power 2 ) = 21 - 9 = 12 ab = 6 . answer is d ."
divide(subtract(21, power(3, 2)), 2)