f(x) = (2-cos^2x-cos^4x)(1+ctg^2x)
[m]f(x)=\frac{2-cos^2x-cos^4x}{sin^2x}[/m]
cos^2x=1-sin^2x
cos^4x=(1-sin^2x)^2=1-2sin^2x+sin^4x
[m]f(x)=\frac{2-1+sin^2x-1+2sin^2x-sin^4x}{sin^2x}[/m]
[m]f(x)=\frac{3sin^2x-sin^4x}{sin^2x}[/m]
[m]f(x)=3-sin^2x[/m]
Так как
[m]-1 ≤ sinx ≤ 1[/m]
и
[m]0 ≤ sin^2x ≤ 1[/m]
[m]-1 ≤- sin^2x ≤ 0[/m]
то
[m]3-1 ≤ 3-sin^2x ≤ 3+0[/m]
[m]2 ≤ 3-sin^2x ≤ 3[/m]
Наименьшее значение функции равно [b]2[/b]
О т в е т. [b]2[/b]