cos2x=1/2,求X等于?已知cos2x=1/2,其中X的取值范围是kπ+π/2到(k+1)π,求X?我算出来是kπ+π/6,答案是kπ+5π/6.为啥呢?求详细说明,

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cos2x=1/2,求X等于?已知cos2x=1/2,其中X的取值范围是kπ+π/2到(k+1)π,求X?我算出来是kπ+π/6,答案是kπ+5π/6.为啥呢?求详细说明,cos2x=1/2,求X等于

cos2x=1/2,求X等于?已知cos2x=1/2,其中X的取值范围是kπ+π/2到(k+1)π,求X?我算出来是kπ+π/6,答案是kπ+5π/6.为啥呢?求详细说明,
cos2x=1/2,求X等于?
已知cos2x=1/2,其中X的取值范围是kπ+π/2到(k+1)π,求X?我算出来是kπ+π/6,答案是kπ+5π/6.为啥呢?求详细说明,

cos2x=1/2,求X等于?已知cos2x=1/2,其中X的取值范围是kπ+π/2到(k+1)π,求X?我算出来是kπ+π/6,答案是kπ+5π/6.为啥呢?求详细说明,
cos(2x)=1/2
2x = 2k'π ± π/3
x = k'π ± π/6
put k-1 = k'
x = (k+1)π ± π/6
x的取值范围是kπ+π/2到(k+1)π
=>x = (k+1)π - π/6 = kπ+5π/6

六分之π比二分之π小啊→_→

∵kπ+π/2∴2kπ+πcos2x=1/2
则2x=2kπ+5π/3
x=kπ+5π/6
你的问题出在2x你以为是在第一象限,其实在第四象限

答:
cos(2x)=1/2
2x=2kπ+π/3或者2x=2kπ-π/3
所以:
x=kπ+π/6或者x=kπ-π/6=(k-1)π+5π/6=Kπ+5π/6
因为:
kπ+π/2<=x<=kπ+π
所以:x=kπ+5π/6