T
thu07102010


bài 1 : 5*[sinx + (cos3x + sỉnx) /( 1+ 2sin2x) ] = cos3x + 3
bài 2 : (sin^4 x+ cos^4 x) / (5sin2x) = 1/2*cot2x - [ (1)/ (8sin2x)]
bài 3 : cos3x*cos^3 x - sỉnx*sin^3 x = [(2+3căn2) / (8)]
bài 2 : (sin^4 x+ cos^4 x) / (5sin2x) = 1/2*cot2x - [ (1)/ (8sin2x)]
bài 3 : cos3x*cos^3 x - sỉnx*sin^3 x = [(2+3căn2) / (8)]