Question

giúp mik với, mik đg gấp

Answer 1

Bài 2:

a: \(\begin{cases}2x+4y=10\\ 3x+5y=13\end{cases}\Rightarrow\begin{cases}6x+12y=30\\ 6x+10y=26\end{cases}\)

=>\(\begin{cases}6x+12y-6x-10y=30-26=4\\ 2x+4y=10\end{cases}\Rightarrow\begin{cases}2y=4\\ x+2y=5\end{cases}\)

=>\(\begin{cases}y=2\\ x=5-2\cdot2=5-4=1\end{cases}\)

b: \(\begin{cases}\left(x+1\right)-5\left(y-2\right)=19\\ 3\left(x+1\right)+2\left(y-2\right)=6\end{cases}\Rightarrow\begin{cases}3\left(x+1\right)-15\left(y-2\right)=57\\ 3\left(x+1\right)+2\left(y-2\right)=6\end{cases}\)

=>\(\begin{cases}3\left(x+1\right)-15\left(y-2\right)-3\left(x+1\right)-2\left(y-2\right)=57-6=51\\ \left(x+1\right)-5\left(y-2\right)=19\end{cases}\)

=>\(\begin{cases}-17\left(y-2\right)=51\\ \left(x+1\right)=19+5\left(y-2\right)\end{cases}\Rightarrow\begin{cases}y-2=-3\\ \left(x+1\right)=19+5\cdot\left(-3\right)=19-15=4\end{cases}\)

=>\(\begin{cases}y=-1\\ x=4-1=3\end{cases}\)

c:

ĐKXĐ: x<>0

\(\begin{cases}\frac{2}{x}+y=3\\ \frac{1}{x}-2y=4\end{cases}\Rightarrow\begin{cases}\frac{4}{x}+2y=6\\ \frac{1}{x}-2y=4\end{cases}\)

=>\(\begin{cases}\frac{4}{x}+2y+\frac{1}{x}-2y=6+4=10\\ \frac{2}{x}+y=3\end{cases}\Rightarrow\begin{cases}\frac{5}{x}=10\\ y=3-\frac{2}{x}\end{cases}\)

=>\(\begin{cases}x=\frac12\left(nhận\right)\\ y=3-2:\frac12=3-4=-1\end{cases}\)

Bài 3:

a: 4x-3>x+9

=>4x-x>3+9

=>3x>12

=>x>4

b: \(\frac{2x+1}{3}-\frac{x-4}{4}\le\frac{3x+1}{6}-\frac{x-4}{12}\)

=>\(\frac{4\left(2x+1\right)}{12}-\frac{3\left(x-4\right)}{12}\le\frac{2\left(3x+1\right)}{12}-\frac{x-4}{12}\)

=>4(2x+1)-3(x-4)<=2(3x+1)-(x-4)

=>8x+4-3x+12<=6x+2-x+4

=>5x+16<=5x+6

=>16<=6(vô lý)

=>Bất phương trình vô nghiệm

c: \(9x^2-2\left(9x+1\right)\ge\left(3x-2\right)^2+18\)

=>\(9x^2-18x-2\ge9x^2-12x+4+18\)

=>-18x-2>=-12x+22

=>-6x>=24

=>x<=-4