Re:두 문제. 질문..

[nunyong]

1. 3sin(x)-sin(x)/cos(x)=0

3-1/cos(x)=0

cos(x)=1/3

sin(x)=2root2/3

cos(a)+sin^2(a)=1/3+8/9=11/9

2. sin^2(30'-20')+sin^2(90'-20')+sin^2(120'-20')+sin^2(180'-20')

=(sin30'cos20'-cos30'sin20')^2+(sin90'cos20'-cos90'sin20')^2+(sin120'cos20'-cos120'sin20')+ (sin180'cos20'-cos180'sin20')^2

=(1/2cos20'-root3/2sin20')^2+(cos20')^2+(root3/2cos20'+1/2sin20')+(sin20')^2

=1/4cos^2(20')+3/4sin^2(20')+cos^2(20')+3/4cos^2(20')+1/4sin^2(20')+sin^2(20')=2sin^2(20')+2cos^2(20')=2



--------------------- [원본 메세지] ---------------------
1. 방정식 3sin(x)-tan(x)=0의 근을 a라 할 때, cos(a)+sin^2(a)의 값은?
(단, 0<a<파이/2)

2. sin^2(10도)+sin^2(70도)+sin^2(100도)+sin^2(160도)의 값은?