sinX+sinY=1 cosX+cosY=0 求cos(2X)+cos(2Y)的值
问题描述:
sinX+sinY=1 cosX+cosY=0 求cos(2X)+cos(2Y)的值
答
消元sinx=1-siny----(1 cosx=-cosy-----(2(1)式^2+(2)式^2-------- 1=(1-siny)^2+cosy^21=1+sin^2y+cos^2y-2siny1=1+1-2sinysiny=1/2sinx=1-1/2=1/2所以cos2x=1-2sin^2x=1-2(1/2)^2=1/2同理cos2y=1/2即cos2x+cos2y...