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Select the appropriate values of x that are solutions to f(x)=0 where f(x)=-7x^2+5x+9

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1 Answer

Since the quadratic equation doesn't factor, you should use the quadratic formula:
                            
x = -b + √b2 - 4ac      a = -7, b = 5. c = 9
              2a
 
                                                                                   
x =  -5 + √52 -4(-7)(9)  =  -5 + √25 + 252  =  -5 + √277
                2(-7)                        -14                     -14
 
x = -5 + 16.6433      and x = -5 - 16.6433
            -14                               -14
 
x = 11.64       and x = -21.64
        -14                       -14
 
x = -.83  and x = 1.55