Даю 35 баллов. Помогите решить 2-4 упражнения.

A2. а) cos (x/2)= - 1/2;         x/2 = + - π/3 + 2πk;         x = + - 2 π/3 + 4  πk; k∈Z.   б)   sin(x + π/4) = 1/2;   x + π/4 =(-1)^(k) ·π/6  + πk; x = (-1)^(k) ·π/6 - π/4 + πk; k∈Z. в) cos x = 4/5;  x = + - arccos(4/5) + 2πk;  k∈Z. г) ctg x = 1/√3; x = π/6 + πk; k∈Z. A3.  а) tg^2 x - 3 tg x - 4 = 0; D = 9+16 = 25 = 5^2;  tg x =4 ;  x= arctg4 + πk; k∈Z. tg x = -1; x = - π/4 + πk; k∈Z. б)  4 sin^2 x - cos x - 1 = 0;      4( 1 - cos^2 x) - cos x - 1 = 0; 4 - 4 cos^2 x - cos x - 1 = 0; 4 cos^2 x + cos x - 3 = 0; D = 1 + 48 = 7^2; cos x= - 1;  x = π+ 2πk; k∈Z. cos x = 3/4; x = + - arccos(3/4) + 2πk; k∈Z. в) cos 2x + cos^2x + sinx·cosx = 0; cos^2 x - sin^2 x + cos^2 x + sinx·cosx= 0; sin^2x - sinx·cosx - 2 cos^2 x= 0;   /:cos^x≠0; tg^2 x - tgx - 2 = 0;  D = 1 + 8 = 3^2; tgx = -1; x = - π/4 + πk; k∈Z; tg x = 2; x = arctg2 + πk; k∈Z. A4. sin x + cos x = √2;   /:√2; 1/√2  ·sinx + 1/√2  · cos x = 1; sin x · cos(π/4) + cos x · sin(π/4) = 1; sin(x + π/4) = 1; x + π/4 = π/2 + 2πk; x = π/2 - π/4 + 2πk; x = π/4 + 2πk; k∈Z.