a: Là hợp số

b: Là hợp số

\(1,\\ a,=\dfrac{7}{6}-\dfrac{4}{3}-\dfrac{1}{2}=-\dfrac{2}{3}\\ b,=\left(-\dfrac{8}{3}\right)\left(12\dfrac{1}{4}-6\dfrac{1}{4}\right)=\left(-\dfrac{8}{3}\right)\cdot6=-16\\ c,=\dfrac{6}{5}-\dfrac{9}{4}\cdot\dfrac{20}{3}+\dfrac{2}{5}=\dfrac{8}{5}-15=-\dfrac{67}{5}\\ 2,\\ a,\Rightarrow x=-\dfrac{1}{2}+\dfrac{11}{4}=\dfrac{9}{4}\\ b,\Rightarrow\left|x+\dfrac{2}{3}\right|=1\Rightarrow\left[{}\begin{matrix}x+\dfrac{2}{3}=1\\x+\dfrac{2}{3}=-1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=-\dfrac{5}{3}\end{matrix}\right.\\ c,\Rightarrow x^2=36\Rightarrow\left[{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\\ 3,f\left(-1\right)=\left(-5\right)\left(-1\right)=5\\ f\left(\dfrac{1}{2}\right)=\left(-5\right)\cdot\dfrac{1}{2}=-\dfrac{5}{2}\)

Bn tk:

\(\Leftrightarrow\left\{{}\begin{matrix}6x+5y=18\\6x+y=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=3\\x=\dfrac{1}{2}\end{matrix}\right.\)

\(\left\{{}\begin{matrix}3x+\dfrac{5}{2}y=9\\2x+\dfrac{1}{3}y=2\left(2\right)\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=3-\dfrac{5}{6}y\left(1\right)\\2x+\dfrac{1}{3}y=2\left(2\right)\end{matrix}\right.\\ Thay\left(1\right)vô\left(2\right)\\ 2\left(3-\dfrac{5}{6}y\right)+\dfrac{1}{3}y=2\\ \Leftrightarrow6-\dfrac{5}{3}y+\dfrac{1}{3}y=2\\ \Leftrightarrow y=3\Rightarrow x=3-\dfrac{5}{6}.3=\dfrac{1}{2}\)

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4: \(=49+139-172+99-139-199+172=49-100=-51\)