Question

giải hệ pt : {3x+y=10

                  {x+y=4

giải pt : x⁴+3x² - 4 =0

Answer 1

\(\left\{{}\begin{matrix}3x+y=10\\x+y=4\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}3x+y-x-y=10-4\\x+y=4\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}2x=6\\x+y=4\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=3\\y=4-x=4-3=1\end{matrix}\right.\)

\(x^4+3x^2-4=0\)

=>\(x^4+4x^2-x^2-4=0\)

=>\(\left(x^2+4\right)\left(x^2-1\right)=0\)

=>\(x^2-1=0\)

=>\(x^2=1\)

=>\(x\in\left\{1;-1\right\}\)