Question

Dada f(x)=x2-8x+14, encontre o valor de x para o qual f(x)=-1

Answer 1

$f(x)=x^2-8x+14\\\\f(x)=-1\\\\x^2-8x+14=-1\\\\x^2-8x+15=0\\\\a=1\\b=-8\\c=15\\\\\triangle=b^2-4ac\\\triangle=(-8)^2-4.(1).(15)\\\triangle=64-60\\\triangle=4\\\\x= \dfrac{-b \frac{+}{-} \sqrt{\triangle} }{2a}\\\\\\x= \dfrac{-(-8) \frac{+}{-} \sqrt{4} }{2} \\\\\\x= \dfrac{8 \frac{+}{-}2 }{2}\\\\\\x'= \dfrac{10}{2}\\\\ \boxed{x'=5} \\\\x"= \dfrac{6}{2}\\\\\boxed{x"=3}$