Katie T.

asked • 12/15/13

Need help bad

Select the approximate values of x that are solutions to f(x) = 0, where f(x)=-8x^2 +9x+5.

A. (-1.60,1.80)

B. (-8,9)

C. (-1.13,-0.63)

D. (-0.41,1.53)
 
I believe the answer is A. My math partner thinks it is D. Who is right and did we miss a step?

Katie T.

Great Tutor!!!!!!
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12/15/13

1 Expert Answer

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Ralph L. answered • 12/15/13

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-8x2 + 9x + 5 = 0
 
a = 8, b = 9, c = 5
 
[-b ± √(b2 - 4ac)]/2a
 
[-9 ± √(92 - 4*-8*5)]/2*(-8)
 
[-9 ± √(81 + 160)]/-16
 
[-9 ± 15.52]/ -16
 
x = -.408 or x =1.53
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Ralph L.

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a should be -8
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12/15/13

Katie T.

Thank you so much Ralph. I did skip some steps and the way you showed me really helped me to understand better. My math partner was right but I will not have a partner when my test comes. I was also confused on the A,B,C values. I really appreciate the way you did all the steps, so I could see this done visually. This has been a great learning experience.  
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12/15/13

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