a: Là hợp số

b: Là hợp số

Bn tk:

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

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

Bạn cần bài nào nhỉ?

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

lỗi rồi bạn ơi:)

write a letter

Hold on

leave a message

on the phone

send cards

makes call

intention

send a fax

send e-mail

surf the internet

old

learn

another

when

over

of

wear

home

write

visited

am going to wash

am going to learn

are going to take

am not going to have

Câu 25: C

Câu 26: B

Câu 27: C