sin+2x等于多少cosx

终巧炕2791sin(2x+90°)等于什么 -
权宜习17642868025 ______ cos(2x)

终巧炕2791sin(2x)+cos(2x)=? -
权宜习17642868025 ______ sin(2x)+cos(2x) =√2[(√2/2)sin2x+(√2/2)cos2x] =√2[sin2xcosπ/4+cos2xsin(π/4)] =√2sin(2x+π/4)

终巧炕2791sin(x+π/4)= - 3/5 sin2x=? -
权宜习17642868025 ______ 这要用到三角函数的公式哦!首先cos(2x+π/2) =- sin2x,cos2x=1-2(sinx)² . 所以sin2x=-cos(2x+π/2)=-cos2(x+π/4)=2 [sin(x+π/4)]² -1= -7/25 这些公式你后面会学到的,现在用到就先说了,加油!!

终巧炕2791已知sin(x+兀/6)=1/3,则sin2x= - -- -
权宜习17642868025 ______ 解:sin(x+ π/6)=[(√3)/2]sinx+(1/2)cosx=1/3, cosx=(2/3)-(√3)sinx, 代入(sinx)^2+(cosx)^2=1 整理得4(sinx)^2-【(4√3)/3】sinx=8/9 解方程得sinx=[(√3)±2√2]/6 cosx=[1-(±2√6)]/6 sin2x=2sinxcosx= -[7√3+4√2]/18或= -[7√3-4√2]/18

终巧炕2791三角函数角度转换sin(2x+π/2)=cos2x么?应该等于多少 -
权宜习17642868025 ______[答案] sin(2x+π/2)=cos2x是对的!

终巧炕2791sin(π/2+x)=1/3,则cos2x= -
权宜习17642868025 ______ sin(π/2+x)=cosx=1/3 所以cos2x=2cos²x-1=-7/9

终巧炕2791若点P(cosα,sinα)在直线y= - 2x上,则sin2α+2cos2α是多少? -
权宜习17642868025 ______ sinα=-2cosα 由sin²α+cos²α=1 可得到cosα=±1/根号(5) sinα=±2/根号(5)(注:cosα和sinα 一正一负) sin2α=2sinαcosα=-4/5 cos2α=2cos²α-1=-3/5 sin2α+2cos2α=-2

终巧炕2791已知函数f(x)= - √3sin^2x+sinxcosx -
权宜习17642868025 ______ f(x)=-√3sin^2x+sinxcosx f(x)=-√3(1-cos2x)/2+sin2x/2 f(x)=-√3/2+√3/2*cos2x+1/2*sin2x f(x)=-√3/2+sin60*cos2x+cos60*sin2x f(x)=-√3/2+sin(60+2x) f(α/2)=1/4-√3/2 f(α/2)=-√3/2+sin(30+α)=1/4-√3/2 sin(30+α)=1/4 sin(30+α) = sin30cosα+cos30...

终巧炕2791sin(π/3+x)=1/3,则sin(π/6+2x)= 我看了几个例题,他们把sin换成了cos 这个是怎么转换的? -
权宜习17642868025 ______ sin(π/6+2x)=-cos(π/2+π/6+2x)=-cos(2π/3+2x)=-cos[2(π/3+x)]=-[1-2sin²(π/3+x)]=-1+2*(1/3)²=--7/9

终巧炕2791sin^2x+cos^2x等于几 -
权宜习17642868025 ______[答案] sin^2x+cos^2x=1 这是公式,要记住