Toán Lớp 7: Cho hàm số y=f(x) = 2-x^2. Tfm x để f(x)=-7
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Toán Lớp 7: Cho hàm số y=f(x) = 2-x^2. Tfm x để f(x)=-7
Comments ( 2 )
y = f(x) = 2 – x^2
f(x) = -7
<=> 2 – x^2 = -7
<=> x^2 = 2 – ( -7 )
<=> x^2 = 9
<=> x ∈ { ±3 }
$Vậy$ x ∈ { ±3 }
Answer
Ta có: y = f(x) = 2 – x^2
Với f(x) = -7
<=> 2 – x^2 = -7
<=> x^2 = 2 + 7
<=> x^2 = 9
<=> x^2 = (+-3)^2
<=> x = +-3
Vậy x \in {3 ; -3}