Question

Answer 1

a: \(x\in\left\{20;-20\right\}\)

b: \(x\in\left\{8;-8\right\}\)

c: \(x\in\varnothing\)

Answer 2

a) \(x^2=400\Rightarrow x=\pm20\)

b) \(x^2-64=0\Rightarrow x^2=64\Rightarrow x=\pm8\)

c) \(5x^2+10=9\Rightarrow5x^2=-1\Rightarrow x^2=-\dfrac{1}{5}\left(VLý\right)\)

Vậy \(S=\varnothing\)