a) t nghĩ là sinx ở cuối là [tex]sin^2 x[/tex]
[tex]A= 1+ sin^2xcos^2x+ cos^4x + sin^2x[/tex]
[tex]A= 1+ cos^2x(1-cos^2x) + cos^4x +sin^2 x[/tex]
A=2
b) [tex]B= sin^2x(\frac{1}{cos^2y}-1)- tan^2y(1- cos^2x)[/tex]
[tex]B= sin^2x(\frac{1}{cos^2y}-1-tan^2y)[/tex]
B=0