tim max

T

thaoteen21

tl

bài 2:
2.cos $\frac{{A + B}}{2}$.cos$\frac{{A - B}}{2}$ - 2.$cos^2$.$\frac{{A + B}}{2}$ + 1 \le $\frac{3}{2}$
\Leftrightarrow $co{s^2}$.$\frac{{A + B}}{2}$ - cos$\frac{{A + B}}{2}$.cos$\frac{{A - B}}{2}$ + $\frac{1}{4}$ \ge 0
\Leftrightarrow $(cos.\frac{A + B}{2} - \frac{1}{2}.cos\frac{A - B}{2})^2$ + $\frac{1}{4}$.${\sin ^2}$.$\frac{{A - B}}{2}$ \geq 0
\Rightarrow đfcm
 
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A

army9x_hn

k phai la kai day. t muon hoi ve cai max cua a+b+c kia co. moi nguoi giup t voi. t dang can gap
 
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