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