For which values of x does the graph of the equation y=-3x^2 +12x -21/2 cross the x-axis.

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justaguide eNotes educator | Certified Educator

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The curve y=-3x^2 +12x -21/2 crosses the x axis when y = 0.

We can determine y = 0 by equating -3x^2 +12x -21/2 to zero

=> -3x^2 +12x -21/2 = 0

multiply by 2

=> -6x^2 + 24x - 21 = 0

divide by -3

=> 2x^2 - 8x + 7 = 0

x1 = [-b + sqrt (b^2 - 4ac )] /2a

=> [ 8 + sqrt (64 - 56)]/4

=> 2 + (sqrt 2)/2

x2 = [ 8 - sqrt (64 - 56)]/4

=> 2 - (sqrt...

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