Question

If x+y=19 and xy=78, find y−x?

Answer 1

xy = 78 (given)

Also, x + y = 19 (given)

Or, (x+y)² = (19)² [squaring both sides]

Or, x² + 2xy + y² = 361

Or, x² + y² = 361 - 156 = 205

Now, (y-x)² = x²+y²-2xy = 205-156 = 49

So, (y-x) = √49 = 7 [ANSWER]