<span>а) tg(-675°) : cos(-570°) - ctg150°
1) tg(-675°)=-tg(675°)=-tg(720°-45°)=-tg(2π-45)=-(-tg 45°)=1
2) cos(-570°)=cos 570°=cos(360+180+30)=cos (2π+π+30)=cos (π+30)=-сos 30=-√3/2
3) ctg 150=ctg(180-30)=ctg(π-30)=-ctg 30=-√3
tg(-675°) : cos(-570°) - ctg150°=1:√3/2+√3=2/√3+√3=2√3/3+√3=5√3/2
б) ctg 43π/6 + sin 28π/3=ctg (7π+π/6)+sin(9π+π/3)=ctg(6π+π+π/6)+sin(8π+π+π/3)=ctg(π+π/6)+sin(π+π/3)=ctg π/6-sin π/3=√3-√3/2=√3/2</span>
А) (4-2b)^2=16-16b+4b^2<span />
решаем через дискриминант. Находим корни и составляем уравнение.
3,21 : 0.3 + 2.42 =10.7 + 2.42 = 13.12
5 : 0.2 - 13 = 25 - 13 = 12
1/4 + 3.17 = 0.25 + 3.17 = 3.42
5/7 + 1/3 + 1/21 = 15/21 + 7/21 - 1/21 = 21/21 = 1
3/5 - 3/8 = 24/40 - 15/40 = 9/40 = 0.225
9/7 : 3/28 = (9 * 28) : (7*3) = 252/21 = 12
2/5 - 0.52 * 5/26 = 0.4 - 2.6/26 = 0.4 -0.1 = 0.3