已知cos^4B-sin^4B=2/3,B属于(0,π/2),则cos(2B+π/3)=?

问题描述:

已知cos^4B-sin^4B=2/3,B属于(0,π/2),则cos(2B+π/3)=?

(2-√15)/6过程有吗cos^4B-sin^4B=(cos^2B+sin^2B)(cos^2B-sin^2B)=cos2B=2/3
sin2B=√5/3
cos(2B+π/3)=1/2*cos2B-√3/2*sin2B