1) sin2B-sin2B*cos2B=?

2) cos4B+cos2B*sin2B=?

3) tg2B*ctg2B-cos2B=?

Sin2B - sin2B*cos2B = sin2B (1 - cos2B) = sin2B (1 - (cos^2 B-Sin^2 B) = sin2B ((1-cos^2 B) + sin^2 B) = sin2B (sin^2 B + sin^2 B) = 2sinB*cosB*2sin^ B = 4sin^3 B*cosB

tg2B*ctg2B-cos2B = 1-cos^2 B + sin^2 B = sin^2 B + sin2 B = 2sin^2 B