a, x+7=-12

\(\Leftrightarrow\) x= -19

b, x-15=-21

\(\Leftrightarrow\) x= -6

c, 13-x=20

\(\Leftrightarrow\) x=-7

a) x+7=-12\(\Leftrightarrow\) x=-12-7\(\Leftrightarrow\) x=-19

b) x-15=-21\(\Leftrightarrow\) x=-21+15\(\Leftrightarrow\) x=-6

c)13-x=20\(\Leftrightarrow\) -x=20-13\(\Leftrightarrow\)-x=7\(\Leftrightarrow\) x=-7

cái này cấp 1 cũng biết ..........

\(a.\)

\(x+7=-12\)

\(\Rightarrow x=-12-7=-19\)

Vậy \(x=-19\)

\(b.\)

\(x-15=-21\)

\(\Rightarrow x=-21+15=-6\)

Vậy \(x=-6\)

\(c.\)

\(13-x=20\)

\(\Rightarrow x=-13-20=-7\)

Vậy \(x-=-7\)

4/1 x 13/15

= 52/15

52/15

mình có câu trl rồi nhé:

4 x 13/15 = 4 x 13/15 = 52/15 nhé!

=>4x=-20

hay x=-5

\(4x+15=-5\)

\(=> 4x=-20\)

\(=>x=-5\)

Vậy \(x=-5\)

\(4x+15=-5.\Leftrightarrow4x=-5-15.\Leftrightarrow4x=-20.\Leftrightarrow x=-5.\)

Chọn A

A

A

14A

15B

16B

17C

18B

19B

20C

\(16.\\ \left\{{}\begin{matrix}P+N+E=76\\P=E\\\left(P+E\right)-N=20\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}2P+N=76\\2P-N=20\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=24\\N=28\end{matrix}\right.\)

\(20.\\ \left\{{}\begin{matrix}P+E+Z=40\\\left(P+E\right)-N=12\\P=E\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}2P+N=40\\2P-N=12\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=13\\N=14\end{matrix}\right.\\ \Rightarrow A=Z+N=13+14=27\left(đ.v.C\right)\)

\(19\\ \left\{{}\begin{matrix}P+E+N=40\\P=E\\\dfrac{N}{P+E}=\dfrac{7}{13}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}2P+N=40\\\dfrac{N}{2P}=\dfrac{7}{13}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}2P+N=40\\13N-14P=0\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=13\\N=14\end{matrix}\right.\\ \Rightarrow A=Z+N=13+14=27\left(đ.v.C\right)\\ \Rightarrow KH:^{27}_{13}R\)

=> Chọn B

Câu 58: B

Câu 59: C