What adds up to -7 but multiplies to 10

X + y = -7
xy = 10















       
       
       

     x + y = -7
  0.9 + y = -7
- 0.9      - 0.9
           y = -7.9
     (x, y) = (0.9, -7.9)

              or

      x + y = -7
  -7.9 + y = -7
+ 7.9        + 7.9
            y = 0.9
      (x, y) = (-7.9, 0.9)

The two numbers that add up to -7 and multiply to -10 are -7.9 and 0.9.