$3sin^{2}2x + 7cos2x = 3$

Em cảm ơn vì đã xem ạ ! Have a good day ! 😍

3(1 - cos^2(2a)) + 7cos2a = 0 ⇔ 3cos^2(2a) - 7cos2a = 0 rồi giải pt bậc hai nhớ loại nghiệm
Oh ! Ra the ! Mik 2k nha ! =)))) –  Christine.st0512 11-07-16 10:41 AM
bn.... mình = tuổi bạn :) –  ≧◔◡◔≦ ۩๖ۣۜNguyễn's Đức♫10x۩ 11-07-16 10:39 AM
D? c�m ?n ? ! –  Christine.st0512 11-07-16 10:37 AM
$Pt\Leftrightarrow 3(1-cos^22x)+7cos2x-3=0\Leftrightarrow -3cos^22x+7cos2x=0\Leftrightarrow cos2x(3cos2x-7)=0\Leftrightarrow cos2x=0$
Do $cos2x\in [-1;1] \Rightarrow 3cos2x-7\leq 0$
Giải $cos2x=0\Leftrightarrow x=\pi /4+k\pi /2$
Da vang a –  Christine.st0512 11-07-16 10:38 AM
Nghia la cam on a ! –  Christine.st0512 11-07-16 10:38 AM
VD : \sin x, \cos x –  tran85295 11-07-16 10:36 AM
mấy cái sin cos thì để dấu \ trước cho dễ nhìn –  tran85295 11-07-16 10:36 AM
j thế??? –  ★·.·´¯`·.·★Poseidon★·.·´¯`·.·★ 11-07-16 10:30 AM
D? c?m ?n anh/ch? / b?n ! –  Christine.st0512 11-07-16 10:28 AM

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