pt luong giac hay ne

H

hoan1793

cos 3x- căn 3 sin 3x=căn 3 cos 2x- sin 2x
<=>1/2 cos 3x- (căn 3/2) sin 3x= ( căn 3/2) cos 2x- 1/2 sin 2x
<=>cos pi/6. cos3x- sin pi/6. sin 3x= cos pi/3. cos 2x- sin pi/3. sin 2x
<=> cos( 3x+ pi/6)= cos (2x+ pi/3)
<=> 3x+pi/6= 2x+ pi/3 + k2pi
hoặc 3x+pi/6= -2x-pi/3+ k2pi
<=> x= pi/6+ k2pi
hoặc x= -pi/10+ kpi/5
 
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