Toán 11 Giải pt Lượng giác

N

niemkieuloveahbu

[TEX]DK: cosx \neq 0\\ PT \Leftrightarrow cos^2x+sinx+cosx=0\\ \Leftrightarrow cosx(cosx+1)+sinx=0\\ \Leftrightarrow 2cos^2{\frac{x}{2}}cosx+2sin{\frac{x}{2}}cos{\frac{x}{2}}=0\\ \Leftrightarrow \[cos{\frac{x}{2}}=0\\ (2cos^2{\frac{x}{2}}-1)cos{\frac{x}{2}}+sin{\frac{x}{2}}=0(*)[/TEX]

(*) : PT đẳng cấp bậc 3
 
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