Question 548518
-56 = (2r-21)(r+1)
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(2r-21)(r+1) = -56
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Use FOIL to expand left side.
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2r^2 +2r -21r -21 = -56
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Add 56 to both sides
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2r^2 +2r -21r -21 +56 = 0
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2r^2 -19r + 35 = 0
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factor
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(2r-5)(r-7) = 0
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roots are r=5/2 and 7
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{{{ graph(500,500,-10,10,-10,10,2*x^2-19*x+35) }}}