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Question 507655: two numbers whose sum is 21 and whose product is 90
Answer by oberobic(2304)   (Show Source):
You can put this solution on YOUR website! x + y = 21
so
x = 21-y
.
x * y = 90
.
substitute
.
(21-y) * y = 90
21y - y^2 = 90
-y^2 +21y - 90 = 0
y^2 -21y + 90 = 0
.
(y -6)(y -15) = 0
.
y = 6 or 15
.
which means
x = 15 or 6, respectively, to make the sum = 21.
.
The two numbers are 6 and 15.
.
Done.
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