Đáp án + Giải thích các bước giải:
`e.`
`sin^4 2x+cos^4 2x=1-2sin4x`
`<=>(sin^2 2x+cos^2 2x)^2-2sin^2 2xcos^2 2x=1-2sin4x`
`<=>1-2sin^2 2xcos^2 2x=1-2sin4x`
`<=>1-1/2(2sin2xcos2x)^2=1-2sin4x`
`<=>1/2 sin^2 4x=2sin4x`
`<=>sin^2 4x-4sin 4x=0`
`<=>`\(\left[ \begin{array}{l}\sin 4x=0\\\sin 4x=4(VN)\end{array} \right.\)
`<=>4x=kpi`
`<=>x=(kpi)/4(kinZZ)`
`f.`
`3/cos^2x=3+2tan^2x`
`<=>3(1+tan^2x)=3+2tan^2x`
`<=>tan^2x=0`
`<=>sin^2x=0`
`<=>sinx=0`
`<=>x=kpi(kinZZ)`
