[theme2010]

ข้อ 42
\[
\begin{array}{l}
(x - 1) + (x - 2) + (x - 1) + (x - 2) = 0 \\
4x - 6 = 0 \\
x = \frac{3}{2} \\
\\
\frac{{ - 13}}{{ - 1/4}} = 2A - 2B \\
52 = 2(A - B) \\
A - B = 26 \\
\end{array}
\]