Given that a\displaystyle {a} is constant such that f(x)=ax42x3+7x29x+4\displaystyle {f{{\left({x}\right)}}}={a}{x}^{{4}}-{2}{x}^{{3}}+{7}{x}^{{2}}-{9}{x}+{4} and that f(2)=4\displaystyle {f{{\left(-{2}\right)}}}=-{4} then find a\displaystyle {a}.

a=\displaystyle {a}=