SOLUTION: Competing the square y=3-15x-3x^2

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Question 983273: Competing the square
y=3-15x-3x^2
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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Competing the square
y=3-15x-3x^2
rearrange to
-3x^2 - 15x + ___ = -3
we want the coefficient of x^2 to be +1, divide equation by -3
x^2 + 5x + ____ = 1
Find the square of half the coefficient of x (5), to complete the square 2.5^2 = 6.25
add to both sides
x^2 + 5x + 6.25 = 1 + 6.25
x^2 + 5x + 6.25 = 7.25
Which is
(x + 2.5)^2 = 7.25
find the square root of both sids
x + 2.5 = +/-sqrt%287.25%29
two solutions
x = -2.5 + sqrt%287.25%29
and
x = -2.5 - sqrt%287.25%29