phuong trinh luong giac

H

hothithuyduong

belunkute_95 said:
de bai ne moi nguoi:-SS:D;)
hay khong kem may bai lan truoc tui gui do:
[TEX]cos^2015 x +sin^2010 x[/TEX]=1
bai biu loi tui noi nha:cos^2015x+sin^2010x=1
Bấm để xem đầy đủ nội dung ...

Do: [TEX]\left{\begin{cos^{2015}x \le \ cos^2x}\\{sin^{2010}x \le \ sin^2x}[/TEX]

[TEX]\leftrightarrow \ cos^{2015}x + sin^{2010}x \le \ cos^2x + sin^2x [/TEX]

[TEX]\leftrightarrow \ cos^{2015}x + sin^{2010}x \le \ 1[/TEX]

Dấu ''='' xảy ra [TEX]\leftrightarrow \ \left{\begin{cos^{2015}x = cos^2x}\\{sin^{2010}x = sin^2x}[/TEX]


 
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N

nguyenhu0ng

Cos^2 15x + sin^2 10x =1
<=> 1 + cos30x +1 – cos20x = 2
<=> -2sin25x sin5x =0
<=> .sin25x =0 <=> x= k2pi/25 v x= pi/25+ k2pi/25
.sin5x = 0 <=>x= k2pi/5 v x= pi/5 + k2pi/5

or: sin 25x = 0 <=> x = kpi/25
sin 5x = 0 <=> x = kpi/5
 
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