toán 11 pt lượng giác

T

trinhhang119

\Leftrightarrow8can2cos^6(x)+2can2sin^3(x)(3sinx-4sin^3(x))-6can2cos^4(x)-1=0
\Leftrightarrow8can2cos^6(x)+6can2sin^4(x)-8can2sin^6(x)-6can2cos^4(x)-1=0
\Leftrightarrow8can2(cos^2(x)-sin^2(x))(cos^4(x)+sin^4(x)+(sinxcosx)^2)+6can2(sin^2(x)-cos^2(x))^2-1=0
\Leftrightarrow8can2cos2x(1-1/4sin^2(2x))-6can2cos2x-1=0
\Leftrightarrow8can2cos2x-2can2cos2x(1-cos^2(2x))-6can2cos2x-1=0
\Leftrightarrow2can2cos^3(2x)-1=0
\Leftrightarrowcos2x=1/can2
đến đây thì chắc giải được rồi nhỉ:)>-
 
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