documentclass[12pt]{article}
usepackage{amsmath}

begin{document}
begin{eqnarray}label{EQ4}
alpha_{0} &=&1-frac{t}{h},  \ nonumber
%
alpha _{1} &=&frac{t}{h},  \ nonumber
%
alpha _{2} &=&frac{1}{2520} frac{756h^{3} +135h}{h^{3}}
-frac{1}{7560} frac{(1869h^{4} +1950h^{2} +70)t}{h^{3} }
+frac{1}{270} frac{left(54h^{3} +15hright)left(frac{5}{2}
t^{2} -frac{3}{2} right)}{h^{3} } \ nonumber &-&
frac{1}{6930} frac{left(715h^{2} +42right)left(frac{7}{2}
t^{3} -frac{5}{2} x+frac{5}{2} x_{n} right)}{h^{3} }
-frac{1}{63} frac{frac{63}{8} t^{4} -frac{35}{4} t^{2}
+frac{15}{8} }{h^{2} } -frac{2}{185} frac{frac{99}{8} t^{5}
-frac{63}{4} t^{3} +frac{35}{8} x-frac{35}{8} x_{n} }{h^{3} },
\ nonumber
%
alpha _{3} &=&-frac{1}{4h^{} } -frac{1}{1260}
frac{left(651h^{4} -900h^{2} -70right)t}{h^{3} } -frac{7}{27}
frac{frac{5}{2} t^{2} -frac{3}{2} }{h^{2} } +frac{2}{1155}
frac{left(165h^{2} +21right)left(frac{7}{2} t^{3}
-frac{5}{2} tright)}{h^{3} } \ nonumber &-& frac{2}{27}
frac{frac{63}{8} t^{4} -frac{35}{4} t^{2} +frac{15}{8} }{h^{2}
} +frac{4}{495} frac{frac{99}{8} t^{5} -frac{63}{4} t^{3}
+frac{35}{8} t}{h^{3} },  \ nonumber

end{eqnarray}
end{document}