Question

Answer 1

a.

\(\Delta=\left(-7\right)^2-4.2.12=-47< 0\)

\(\Rightarrow\) Phương trình đã cho vô nghiệm

b.

Đặt \(x^2=t\ge0\) ta được:

\(t^2-15t-16=0\)

\(\Leftrightarrow\left(t+1\right)\left(t-16\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}t=-1< 0\left(loại\right)\\t=16\end{matrix}\right.\)

\(\Rightarrow x^2=16\Rightarrow x=\pm4\)

c.

\(\left\{{}\begin{matrix}3x-y=10\\x+y=2\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}4x=12\\x+y=2\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=3\\y=2-x\end{matrix}\right.\)

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