The sum of the real numbers x and y is 15. their difference is 3. what is the value of xy?

X+y=15,

x-y=3

the easiest way is the find out x and y first:

add up the two equations: 2x=18, x=9

plug x=9 in either equation, you get y=6

so xy=6*9=54

Another way to do it:

(x+y) ²=15²=225 = >x²+2xy+y²=225

(x-y) ²=3²=9 = >x²-2xy+y²=9

subtract one equation from the other: 4xy=225-9=216, xy=54

X=9 and y=6 because 6 plus 9 does equal 15 and the difference of these two numbers is 3