a)[TEX]\frac{1}{1 + sin^2x} + \frac{1}{cos^2x} = \frac{32}{15}[/TEX]
câu 1
[TEX]\frac{1}{1 + sin^2x} + \frac{1}{cos^2x} = \frac{32}{15}[/TEX]
\Leftrightarrow[TEX] \frac{15(1 - sin ^2x + 1 + sin^2x)} {1- sin^4x} = 32[/TEX]
\Leftrightarrow [TEX]15(1 - sin ^2x + 1 + sin^2x) = 32(1- sin^4x)[/TEX]
\Leftrightarrow [TEX]30 = 32 - 32sin^4x = 0[/TEX]
\Leftrightarrow[TEX] (2sinx)^4 - 1 = 0 [/TEX]