c) Đề sai
d) $\tan(a+b) = 1 \iff \tan a + \tan b = 1 - \tan a \tan b \iff (1+\tan a)(1 + \tan b) = 2$
e) $B = \sqrt{\sin^2 a + \sin a \cos a + \cos^2 a + \sin a \cos a} = |\sin a + \cos a|$
c) Đề sai
d) $\tan(a+b) = 1 \iff \tan a + \tan b = 1 - \tan a \tan b \iff (1+\tan a)(1 + \tan b) = 2$
e) $B = \sqrt{\sin^2 a + \sin a \cos a + \cos^2 a + \sin a \cos a} = |\sin a + \cos a|$