lucky+five+since1997
@郎呢890：高一数学 cos^2(π/5)+sin^2(π/10) 求值 -
朱凤18198084074…… 高一数学 cos²(π/5)+sin²(π/10) 求值 解:先求cos(π/5),即cos36⁰的值.cos36⁰=1-2sin²18⁰;又cos36⁰=sin54⁰=3sin18⁰-4sin³18⁰;故得1-2sin²18⁰=3sin18⁰-4sin³18⁰;即有4sin³18⁰-2sin²18⁰-3sin18⁰+1=0 分解因式:4...
@郎呢890：用＂五点法＂作图时,正弦型函数y=1/2sin(1/3x+π/4)对应的五个关键点分别为? - 作业帮
朱凤18198084074…… [答案] 最大:(1/3x+π/4)=π/2,y=1/2 最小:(1/3x+π/4)=3π/2,y=-1/2 零点:(1/3x+π/4)=0,π,2π,y=0
@郎呢890：C语言:程序功能是:对x=1,2,3,……10,求f(x)=x*x - 5*x+sin(x)的最大值 -
朱凤18198084074…… 1-5+sin(1) //下面for从2开始说明默认最大值为f(1) x*x-5*x+sin(x)>max
@郎呢890：化简:[cos(α - 5π)+2sin(3π - α)]/[csc(3π+α)+sec(5π+α)] - 作业帮
朱凤18198084074…… [答案] [cos(α-5π)+2sin(3π-α)]/[csc(3π+α)+sec(5π+α)]=[cosacos5π+sinasin5π+2(sin3πcosa-cos3πsina)]/[1/sin(3π+a)+1/cos(5π+a)]=[-cosa+2sina]/[-1/sina-1/cosa]=(-cosa+2sina)*sinacosa/(-cosa-sina)=(-1...
@郎呢890：sin5ºcos25º+sin85ºcos65º= - 作业帮
朱凤18198084074…… [答案] sin5º=sin(90º-85º)=cos85º cos25º=cos(90º-65º)=sin65º ∴sin5ºcos25º+sin85ºcos65º =cos85ºsin65º+sin85ºcos65º =sin(65º+85º) =sin150º =1/2
@郎呢890：y=sin(3x+5)的导数怎么求 - 作业帮
朱凤18198084074…… [答案] y'=sin'(3x+5)*(3x)'=3cos(3x+5)
@郎呢890：6! - 5! - 4! - 3! - 49+sin兀/2=多少 -
朱凤18198084074…… 6!-5!-4!-3!-49+sin(π/2)=720 -120-24-6 -49 +1=522
@郎呢890：已知a是第一象线的角,且cosa=5/13,求sin(a+π/4)/cos(2a+4π) - 作业帮
朱凤18198084074…… [答案] 已知a是第一象限的角,且cosa=5/13,求sin(a+π/4)/cos(2a+4π)sin(a+π/4)/cos(2a+4π)=(√2/2)(sinα+cosα)/cos2α=(sinα+cosα)/(cos²α-sin²α)=1/(cosα-sinα)=1/[5/13-√(1-25/169)]=1/[(5/13)-(12...
@郎呢890：f(x)=sin(2x - 5/6π)+2cos2x化简并求出f(x)的单调增区间 - 作业帮
朱凤18198084074…… [答案] 解析: f(x)=sin(2x-5/6π)+2cos2x =sin2x*cos(5/6π)- cos2x*sin(5/6π) +2cos2x =sin2x*[-cos(π/6)] -cos2x*sin(π/6) +2cos2x =sin2x*(-√3/2) - cos2x*(1/2) +2cos2x =sin2x*(-√3/2) - cos2x*(3/2) =-√3*[sin2x*(1/2) +cos2x*(√3/2)] =-√3*sin(2x+ π/3) 则可知当π/2...
@郎呢890：已知2cosα+sinα=√5 求sinα的值 - 作业帮
朱凤18198084074…… [答案] 2cosα+sinα=√5 2cosα=√5-sinα 2(cosα)^2=5+(sinα)^2- 2√5sinα 3(sinα)^2- 2√5sinα +3 =0 sinα = (2√5 -√2)/6 or (2√5 +√2)/6
朱凤18198084074…… 高一数学 cos²(π/5)+sin²(π/10) 求值 解:先求cos(π/5),即cos36⁰的值.cos36⁰=1-2sin²18⁰;又cos36⁰=sin54⁰=3sin18⁰-4sin³18⁰;故得1-2sin²18⁰=3sin18⁰-4sin³18⁰;即有4sin³18⁰-2sin²18⁰-3sin18⁰+1=0 分解因式:4...
@郎呢890：用＂五点法＂作图时,正弦型函数y=1/2sin(1/3x+π/4)对应的五个关键点分别为? - 作业帮
朱凤18198084074…… [答案] 最大:(1/3x+π/4)=π/2,y=1/2 最小:(1/3x+π/4)=3π/2,y=-1/2 零点:(1/3x+π/4)=0,π,2π,y=0
@郎呢890：C语言:程序功能是:对x=1,2,3,……10,求f(x)=x*x - 5*x+sin(x)的最大值 -
朱凤18198084074…… 1-5+sin(1) //下面for从2开始说明默认最大值为f(1) x*x-5*x+sin(x)>max
@郎呢890：化简:[cos(α - 5π)+2sin(3π - α)]/[csc(3π+α)+sec(5π+α)] - 作业帮
朱凤18198084074…… [答案] [cos(α-5π)+2sin(3π-α)]/[csc(3π+α)+sec(5π+α)]=[cosacos5π+sinasin5π+2(sin3πcosa-cos3πsina)]/[1/sin(3π+a)+1/cos(5π+a)]=[-cosa+2sina]/[-1/sina-1/cosa]=(-cosa+2sina)*sinacosa/(-cosa-sina)=(-1...
@郎呢890：sin5ºcos25º+sin85ºcos65º= - 作业帮
朱凤18198084074…… [答案] sin5º=sin(90º-85º)=cos85º cos25º=cos(90º-65º)=sin65º ∴sin5ºcos25º+sin85ºcos65º =cos85ºsin65º+sin85ºcos65º =sin(65º+85º) =sin150º =1/2
@郎呢890：y=sin(3x+5)的导数怎么求 - 作业帮
朱凤18198084074…… [答案] y'=sin'(3x+5)*(3x)'=3cos(3x+5)
@郎呢890：6! - 5! - 4! - 3! - 49+sin兀/2=多少 -
朱凤18198084074…… 6!-5!-4!-3!-49+sin(π/2)=720 -120-24-6 -49 +1=522
@郎呢890：已知a是第一象线的角,且cosa=5/13,求sin(a+π/4)/cos(2a+4π) - 作业帮
朱凤18198084074…… [答案] 已知a是第一象限的角,且cosa=5/13,求sin(a+π/4)/cos(2a+4π)sin(a+π/4)/cos(2a+4π)=(√2/2)(sinα+cosα)/cos2α=(sinα+cosα)/(cos²α-sin²α)=1/(cosα-sinα)=1/[5/13-√(1-25/169)]=1/[(5/13)-(12...
@郎呢890：f(x)=sin(2x - 5/6π)+2cos2x化简并求出f(x)的单调增区间 - 作业帮
朱凤18198084074…… [答案] 解析: f(x)=sin(2x-5/6π)+2cos2x =sin2x*cos(5/6π)- cos2x*sin(5/6π) +2cos2x =sin2x*[-cos(π/6)] -cos2x*sin(π/6) +2cos2x =sin2x*(-√3/2) - cos2x*(1/2) +2cos2x =sin2x*(-√3/2) - cos2x*(3/2) =-√3*[sin2x*(1/2) +cos2x*(√3/2)] =-√3*sin(2x+ π/3) 则可知当π/2...
@郎呢890：已知2cosα+sinα=√5 求sinα的值 - 作业帮
朱凤18198084074…… [答案] 2cosα+sinα=√5 2cosα=√5-sinα 2(cosα)^2=5+(sinα)^2- 2√5sinα 3(sinα)^2- 2√5sinα +3 =0 sinα = (2√5 -√2)/6 or (2√5 +√2)/6
