歌唱祖国大合唱mv 超清:设a=（cos x/2,sinx/2) b=(sin3x/2,sin3x/2) x∈[0, pai/2]

来源：百度文库编辑：高校问答时间：2024/05/14 09:26:35

设a=（cos x/2,sinx/2) b=(sin3x/2,sin3x/2) x∈[0, pai/2]
（1）若a‖b，求x的值.
（2）求|a+b|的取值范围.

解.（1）∵a‖b
∴cosx/2cos3x/2-sinx/2sin3x/2=0
即cos2x=0
∵x∈[0,π/2 ]
∴x=pai/4
(2)|a+b|^2 =|a|^2 +|b|^2 =2a•b=2+2sin2x
∵x∈[0,pai/2 ]
∴2x∈[0,π]
2+2sin2x∈[2,4]
∴|a+b|∈[sqr2 ,2]

22222

设a=（cos x/2,sinx/2) b=(sin3x/2,sin3x/2) x∈[0, pai/2] 求证：sin(2x+y)/sinx-2cos(x+y)=siny/sinx a为何值,sin^2x＋2sinx*cosx-2cos^2x=a有实数解用数学归纳法证明:cos(x/2)×cos(x/2^2)×...×cos(x/2^n)=sinx/[2^n×sin(x/2^n)] 用数学归纳法证明:cos(x/2)×cos(x/2^2)×...×cos(x/2^n)=sinx/[2^n×sin(x/2^n)] 已知(4sin^2) x-(cos^2)x-6sinx+3cosx=0,求(cos2x-cos^2 x)/(1-cot^2 x)的值已知(4sin^2) x-(cos^2)x-6sinx+3cosx=0,求(cos2x-cos^2 x)/(1-cot^2 x)的值已知(4sin^2) x-(cos^2)x-6sinx+3cosx=0,求(cos2x-cos^2 x)/(1-cot^2 x)的值。已知(4sin^2) x-(cos^2)x-6sinx+3cosx=0,求(cos2x-cos^2 x)/(1-cot^2 x)的值。求满足cos(πsinx)=1/2的角x的集合