( 1)3+cos4a-4cos2a=3+2cos2a^2- 1-4cos2a=2( 1+cos2a^2-2cos2a)=2( 1-cos2a)^2=2(2sina^2)^2=8sina^4

(3) tan(x/2+π/4)+tan(x/2-π/4)

=[tan(x/2)+tan(π/4)]/[ 1-tan(x/2)tan(π/4)]+[tan(x/2)-tan(π/4)]/[ 1+tan(x/2)tan(π/4)]

=[tan(x/2)+ 1]/[ 1-tan(x/2)]+[tan(x/2)- 1]/[ 1+tan(x/2)]

=[(tan(x/2)+ 1)^2-(tan(x/2)- 1)^2]/[ 1-(tan(x/2))^2]

=4tan(x/2)/[ 1-(tan(x/2))^2]

=4tan(x/2)/[ 1-(tan(x/2))^2]=2{tan(x/2)+tan(x/2)/[ 1-(tan(x/2))×(tan(x/2))]}

=2tanx