2 cos 2 ( π 4 − 2 x ) + √ 3 cos 4 x = 4 cos 2 x − 1
2 câu trả lời
2cos2(Π4−2x)=2(cosΠ4.cos2x+sinΠ4.sin2x)2=(cos2x+sin2x)2=1+2cos2x.sin2x=1+sin4x2cos2(Π4−2x)=2(cosΠ4.cos2x+sinΠ4.sin2x)2=(cos2x+sin2x)2=1+2cos2x.sin2x=1+sin4x
=> được phương trình tương đương:
1+sin4x+√3cos4x=4cos2x−1<=>sin4x+√3cos4x=4cos2x−2=2cos2x<=>12sin4x+√32cos4x=cos2x<=>cos(4x−Π6)=cos2x
