sin2x-cos2x=根号2sin(2x-π/4) 为什么啊

问题描述:

sin2x-cos2x=根号2sin(2x-π/4) 为什么啊

sin2x-cos2x=√2(√2/2sin2x-√2/2cos2x)
=√2(sin2xcosπ/4-cos2xsinπ/4)
=√2sin(2x-π/4)=√2(sin2xcosπ/4-cos2xsinπ/4)怎么弄的那个√2就是sin2x与cos2x系数的平方根