Помогите решить Найдите область значений функции а) y(x)=sin3x б) y(x)=4cosx-9 в) y(x)=-4x (в квадрате)+1000

[latex]y=sin(3x)[/latex] [latex]-1 \leq sin A \leq 1[/latex] [latex]-1 \leq sin (3x) \leq 1[/latex] [latex]E(y)=[-1;1][/latex] --------------------------------------- [latex]y=4cos x-9[/latex] [latex]-1 \leq cos A \leq 1[/latex] [latex]-1 \leq cos x \leq 1[/latex] [latex]4*(-1) \leq 4*cos x \leq 4*1[/latex] [latex]-4 \leq 4cos x \leq 4[/latex] [latex]-4-9 \leq 4cos x-9 \leq 4-9[/latex] [latex]-13 \leq 4cos x-9 \leq -5[/latex] [latex]E(y)=[-13;-5][/latex] ---------------------- [latex]y=-4x^2+1000[/latex] [latex]x^2 \geq 0[/latex] [latex]-x^2 \leq 0[/latex] [latex]-4x^2 \leq 4*0[/latex] [latex]-4x^2 \leq 0[/latex] [latex]-4x^2 +1000 \leq 0+1000[/latex] [latex]-4x^2+1000 \leq 1000[/latex] [latex]E(y)=(-\infty;1000][/latex]