sin2x=2sinxcosx,那sin3x.sin4x.5x.6x.呢?怎麼推出来的?还有cos2x=1-(2sinx)^2 or (2cosx)^2-1,那3x.4x.5x.6x 等等呢?

sin^2x=2sinxcosx=sin2x吗? 为什么2sinxcosx=sin2x? 为什么sin2x=2sinxcosx 1-cos2x+sin2x= -2sin^x+2sinxcosx应该是等于 2sin^x+2sinxcosx吧? 2sinx^2-sinxcosx-3cosx^2=0 求sin(x+45)/(sin2x+cos2x+1) 2sinx-cosx=0 求sin2x和 sin^2+sinxcosx cos²x+sin²x-2sinxcosx=1-sin2x怎么算出来的呢! 化简：y=cos2x+2sinxcosx-sin2x 用欧拉公式证明sin2x=2sinxcosx 2sinxcosx=sin2x?怎么算啊 2sinxcosx=sin2x?怎么算啊 三角函数数学题已知2sin^2+sinXcosX-4sinX-2cosX=0,求（1+sin2X)/(1-cos2X)(1-tan2X)应该是：已知2sin^2X+sinXcosX-4sinX-2cosX=0,求（1+sin2X)/(1-cos2X)(1-tan2X) sinx+cosx+sinxcosx+1=√2*sin(x+π/4)+1/2 *sin2x+1是为什么? 已知2sin²x-cos²x+sinxcosx-4sinx+2cosx=0求(sin2x+1)/(1+cos2x+sin2x) y=sin^2x-3sinxcosx+4cos^2x是否等于y=sin^2x+cos^2x+3cos^2x-3/2*sin2x?y=sin^2x-3sinxcosx+4cos^2xy=sin^2x+cos^2x+3cos^2x-3/2*sin2x=1+3cos^2x-3/2*sin2x=1+3（1-sin^2x）-3/2*sin2x=-3sin^2x-3/2*sin2x+4 2√3sinxcosx+2cos²x-1 =√3sin2x+cos2x =2sin(2x+π/6)2√3sinxcosx+2cos²x-1 怎么变成 √3sin2x+cos2x 的啊? 求证：:(1-2sin2x·coax)/(cos²x-sin²x)=(cos^2x-sin^2x）/(1+2sinxcosx) 已知x∈（0,π/2）,2sin^2(x)-sinxcosx-3cos^2x=0,求sin(x+π/4)/sin2x+cos2x+1的值.