5 x y - 7 = 8 + 2 x y
5 x y - 7 - 2 x y = 8
( 5 x y - 2 x y ) - 7 = 8
3 x y - 7 = 8
3 x y = 8 + 7
3 x y = 15
y = 15 : 3
y = 5
Vậy ...
\(5\times y-7=8+2\times y\)
\(5\times y-7-2\times y=8\)
\(\left(5\times y-2\times y\right)-7=8\)
\(3\times y-7=8\)
\(3\times y=8+7\)
\(3\times y=15\)
\(y=15\div3\)
\(y=5\)