sin|a|+cos|a|>=0求证!急

求证sin(90+a)=cos a 求证:sin a (1+cos2a)=sin a cos a 求证：tan a/2＝(1-cos)/sin a=sin a/(cos a+1) 求证sin^4a-cos^4a=-cos2a 求证:cos(a+b)cos(a-b)=cos平方b-sin平方a 求证:sin a(1+tan a)+cos a(1+1/tan a)=1/sin a+1/cos a 已知cos(a+B)+1=0,求证sin(2a+B)+sinB=0?(提示:sin(-a)=-sina). 已知cos(a+b)=0,求证：sin(a+2b)=sina 已知COS(A+B)=0 求证SIN(A+2B)=SINA 求证：cos²x+cos²(x+a)-2cosxcosacos(x+a)=sin³a 求证sin^4a+cos^4a=1-2sin²acos²a 求证 cos（A）+ 根号3sin(A)=2sin(π/6+A)