SOLUTION: What adds to make 5 and multiplies to get -3

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Question 770348: What adds to make 5 and multiplies to get -3
Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
What adds to make 5 and multiplies to get -3
Let x and y be the answers:

x + y = 5
   xy = -3

Solve the first for y

    y = 5 - x

Substitute it in the second

   xy = -3

x(5 - x) = -3

5x - x² = -3

0 = x² - 5x - 3

Use the quadratic formula since that doesn't factor:

x = %28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ 

x = %28-%28-5%29+%2B-+sqrt%28+%28-5%29%5E2-4%2A%281%29%2A%28-3%29+%29%29%2F%282%2A%281%29%29+

x = %285+%2B-+sqrt%2825%2B12+%29%29%2F2+

x = %285+%2B-+sqrt%2837%29%29%2F2+

That's two answers:

 x = %285+%2B+sqrt%2837%29%29%2F2+ and x = %285+-+sqrt%2837%29%29%2F2+

Substituting in y = 5 - x

 y = 5 - %285+%2B+sqrt%2837%29%29%2F2+  and y = 5 - %285+-+sqrt%2837%29%29%2F2+ 

y = 10%2F2 - %285+%2B+sqrt%2837%29%29%2F2+  and y = 10%2F2 - %285+-+sqrt%2837%29%29%2F2+ 

     y = %285+-+sqrt%2837%29%29%2F2+  and y = %285+%2B+sqrt%2837%29%29%2F2+

So there is really only one solution since 
those just reverse the roles of x and y.

Answer: %285+%2B+sqrt%2837%29%29%2F2+  and  %285+-+sqrt%2837%29%29%2F2+

Checking:

Add them:

%285+%2B+sqrt%2837%29%29%2F2+%22%22%2B%22%22%285+-+sqrt%2837%29%29%2F2+ %22%22=%22%22%2810+%2B+sqrt%2837%29-sqrt%2837%29%29%2F2+ %22%22=%22%22  10%2F2 %22%22=%22%22 5.

Multiply them:

%285+-+sqrt%2837%29%29%2F2+%22%22%2A%22%22%285+%2B+sqrt%2837%29%29%2F2+ %22%22=%22%22 %2825+-+37%29%2F4 %22%22=%22%22 %28-12%29%2F4 %22%22=%22%22 -3.

Edwin