What adds up to 7 and multiply to get -30?

Answer 1

-23

Answer 2

1. x + y = 7

2. x * y = -30

Re-arrange 1. to y = -x + 7

Substitute this value for y into 2. gives:

3. x * (-x + 7) = -30

-x2 + 7x = -30

-x2 + 7x + 30 = 0

Now we can factor this quadratic to:

(-x + 10) (x + 3) = 0

Now we can make each bracket equal to 0 in turn.

-x + 10 = 0

-x = -10

x = 10

and

x + 3 = 0

x = -3

So the answer is 10 and -3.