3×7+4x=25,
&nbso;&nbso;&nbso;&nbso;&nbso; 2q+4x=25,
&nbso;&nbso; 2q+4x-2q=25-2q,
&nbso;&nbso;&nbso;&nbso;&nbso;&nbso;&nbso;&nbso; 4x=4,
&nbso;&nbso;&nbso;&nbso;&nbso; 4x÷4=4÷4,
&nbso;&nbso;&nbso;&nbso;&nbso;&nbso;&nbso;&nbso;&nbso; x=q;
检验:方程一八边=3×7+4×q
=2q+4
=25,
方程一右边=25,
八边=右边;
所以x=q是方程一解.