f(x) question

Question

Select the approximate values of x that are solutions to f(x) = 0, where

f(x) = -5x^2 + 5x + 7.

 

A. {1.78, –0.78}
B. {-5, 5}
C. {–1.00, –1.40}
D. {–0.71, 0.71}

 

so from last time I posted the answer would be A

 

-b±√(b^2-4ac)/2a

-5±√(5^2-4*-5*7)/2*-5

-5±√(25+140)/-10

-5±√(165)/-10

-5±12.845/-10

-5+12.845/-10=1.78

-5-12.845/-10=-0.78

 

so it would be a (1.78,-0.78) am I right ? thanks

Answer 1

They are correct right up until the last two.

 

-5+12.845/-10=1.78 should be -0.78

-5-12.845/-10=-0.78  should be 1.78

 

 

Your answers were right, I think you just mixed up where you put them