I hope this helps you
A) a=sin t/cos t=(sint*cost)|cos^2t
sin t * cos t= a*cos^2 t
a^2=(1/cos^2 t)-1 cos^2t=1/(a^2+1)
sin t * cos t= a/(a^2+1)
B) sin^4 t=(1-cos^ t)^2
sin^4 t=(1-1/(a^2+1))^2
sin^4 t = a^4/(a^2+1))^2
I hope this helps you
A) a=sin t/cos t=(sint*cost)|cos^2t
sin t * cos t= a*cos^2 t
a^2=(1/cos^2 t)-1 cos^2t=1/(a^2+1)
sin t * cos t= a/(a^2+1)
B) sin^4 t=(1-cos^ t)^2
sin^4 t=(1-1/(a^2+1))^2
sin^4 t = a^4/(a^2+1))^2