##第二章3角函数
- 2π=360度,弧度与角度
- sin(Ѳ)=对边/斜边,con(Ѳ)=临边/斜边,tan(Ѳ)=sin(Ѳ)/cos(Ѳ)
- csc(Ѳ)=1/sin(Ѳ),sec(Ѳ)=1/cos(Ѳ),cot(Ѳ)=1/tan(Ѳ)
- sin(π/6) = 1/2 =cos(π/3),sin(π/3)=cos(π/6)=根号3/2;
- 三角函数的第一象限到第四象限,通过找到参考角获得他的sin,cos值等,根据ASTC获得正负
- 三角函数的图像sin奇函数,cos偶函数,tan奇函数
- cos(x)²+sin(x)²=1;
- 1 + tan(x)² = sec(x)²;
- cot(x)²+1 = csc(x)²;
- sin(A+B)=sin(A)cos(B)+cos(A)sin(B);
- cos(A+B)=cos(A)cos(B) -sin(A)sin(B);
- sin(2x) =2sin(x)cos(x)
- cos(2x)=2cos(x)²-1 =1.2sin(x)²