\documentclass[11pt]{book}
\usepackage{amsmath}
\usepackage{xepersian}
\settextfont{Yas}
\setdigitfont{Yas}
\begin{document}
\begin{align*}
y''+y &= 2A_1 \cos x -2(A_0+2A_1x)\sin x - (A_0x+A_1 x^2)\cos x \\
&+2 B_1\sin x + 2(B_0 + 2B_1 x)\cos x - (B_0 x+ B_1 x^2) \sin x \\
& + (A_0 x + A_1 x^2) \cos x + (B_0 x + B_1 x^2) \sin x = \cos x + x \sin x \\
&\Rightarrow [ (2A_0 + 2B_0) + 4 B_1 x] \cos x + [(-2A_0 + 2B_1-B_0) + (B_0 -4 A_1) x] \sin x \\
&= cos x + x \sin x
\end{align*}
\end{document}