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Quadratic Formula

Select the approximate values of x that are solutions to f(x)=0, where f(x)=-9x^2+5x+7
A. (1.20,-0.65)
B. (-9,5)
C. (-0.56,-0.78)
D. (-1.29,0.71)

1 Answer by Expert Tutors

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John L. | Math, Science, CAD, Engineering TutorMath, Science, CAD, Engineering Tutor
4.9 4.9 (18 lesson ratings) (18)
I find that having the (-) on the x2 can sometimes make the quadratic formula confusing, as having the correct sign on the a,b, and c values is critical to get the correct answer. Multiply the whole equation by -1 and give the quadratic equation another shot!
The discriminant: b- 4*a*c is also a very helpful tool for solving polynomials.
Hope this helps!