Здесь формула тангенса двойного угла
= tg 30 = 1/√3
√(3-6x)=√(3-6*0,5)=√(3-3)=<span>√0=0</span>
1) 2х^3-50=0
2x³=50
x³=25
x=∛25
Ответ x=∛25
2)16х^3+8х+х=0
16x³+9x=0
x(16x²+9)=0
x=0
16x²+9>0 при любом х
Ответ х=0
1)sin15°=sin(45-30)=sin45*cos30-cos45*sin30=√2/2(sin45)*√3/2(cos30)-√2/2(cos45)*1/2(sin30)=√6/4-√2/4=(√6-√2)/4
sin75°=sin(45+30)=sin45*cos30+cos45*sin30=√2/2(sin45)*√3/2(cos30)+√2/2(cos45)*1/2(sin30)=√6/4+√2/4=(√6+√2)/4
(√6-√2)/4-(√6+√2)/4=(√6-√2-√6-√2)/4=-2√2/4=-√2/2
2)cos15°+cos165°=
cos15°=cos(45-30)=cos45*cos30-sin45*sin30=√2/2(cos45)*√3/2(cos30)-√2/2(sin45)*1/2(sin30)=√6/4-√2/4=(√6-√2)/4
cos165=cos(90+75)=-sin75=-sin(45+30)=-(sin45*cos30+cos45*sin30)=-(√2/2(sin45)*√3/2(cos30)+√2/2(cos45)*1/2(sin30))=-(√6/4+√2/4)=(-√6-√2)/4
(√6-√2)/4+(-√6-√2)/4=(√6-√2-√6-√2)/4=-2√2/4=-√2/2
3)
Решение
sin25° ≈ 0,4226<span>0</span>
sin31° ≈ 0,5150
sin47° ≈ 0;7314
cos25° ≈ 0,9063
cos31° ≈ 0,8572
cos47° ≈ 0,6820