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 \(x-=-7\)