Answer:
x = -5/6, +4/3
Step-by-step explanation:
You want to look for two factors of 18·(-20) = -360 that have a sum of -9. They are -24 and +15. These let you rewrite the middle term as two terms:
y = 18x^2 -24x +15x -20
Now, you can factor by grouping the terms 2 at a time.
y = 6x(3x -4) +5(3x -4)
y = (6x +5)(3x -4)
These factors are zero when y = 0, so the zeros are ...
x = -5/6 and x = 4/3
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Sometimes when I'm really stumped with roots of polynomials, I use a graphing calculator to find them.
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Factors of -360 are ...
-360 = -360·1 = -180·2 = -120·3 = -90·4 = -72·5 = -60·6 = -45·8 = -40·9 = -36·10 = -30·12 = -24·15 = -20·18
