[tex] f (x) = 16x ^ 4 - 9x ^ 2 \\ \\16x ^ 4 - 9x ^ 2=0\\ \\x^2(16x^2-9)=0 \\ \\x^2 =0 \ \ or \ \ 16x^2-9=0\\ \\ x=0 \ \ or \ \ (4x-3)(4x+3)=0\\ \\ x=0 \ \ or \ \ 4x-3=0 \ \ or \ \ 4x+3 =0\\ \\x=0 \ \ or \ \ 4x=3 \ \ / :4 \ \ or \ \ 4x=-3\ \ / :4 \\ \\ x=0 \ \ or \ \ x=\frac{3}{4} \ \ or \ \ x=-\frac{3}{4} [/tex]