12 - 25Сos²(П - a)tg²( 2П - a) = 12 - 25Cos²atg²a = 12-25Cos²a * Sin²a/Cos²a =
= 12 - 25Sin²a если Sina = 1/ 2√5, то
12 - 25 * (1/ 2√5)² = 12 - 25 * 1/20 = 12 - 5/4 = 12 - 1,25 = 10,75
-2sin(3x/2)sin(5x/2)=0
sin(3x/2)=0
3x/2=πk
x=2πk/3
0≤2πk/3≤4π
0≤2k≤12
0≤k≤6
k=0 x=0
k=1 x=2π/3
k=2 x=4π/3
k=3 x=2π
k=4 x=8π/3
k=5 x=10π/3
k=6 x=4π
sin(5x/2)=0
5x/2=πk
x=2πk/5
0≤2πk/5≤4π
0≤2k≤20
0≤k≤10
k=0 x=0
k=1 x=2π/5
k=2 x=4π/5
k=3 x=6π/5
k=4 x=8π/5
k=5 x=2π
k=6 x=12π/5
k=7 x=14π/5
k=8 x=16π/5
k=9 x=18π/5
x=10 x=4π
<span>а) ВВ1, СС1, DD1;
б) AD, AB, A1D1, A1B1;
в) DC, BC, D1C1, B1C1;
г) DD1C1C, BB1C1C;
д) ABCD, A1B1C1D1;
ж) AA1D1D, DD1C1C, CC1B1B, AA1B1B;
з) </span>∠<span>(AC1, ABC)=C1AC;
и) </span>∠<span>D1AD.</span>