Giải phương trình

H

hn3

[TEX]sin(\frac{5x}{2})=5.cos^3x.sin(\frac{x}{2})[/TEX]

Ta có : [TEX]sin(\frac{5x}{2})=sin(\frac{x}{2}+2x)=sin(\frac{x}{2}).cos2x+cos(\frac{x}{2}).sin2x=sin(\frac{x}{2}).cos2x+4.cosx.cos^2(\frac{x}{2}).sin(\frac{x}{2})[/TEX]

Vậy , phương trình ban đầu trở thành :

[TEX]sin(\frac{x}{2}).cos2x+4.sin(\frac{x}{2}).cos^2 (\frac{x}{2}).cosx-5.sin(\frac{x}{2}).cos^3x=0[/TEX]

[TEX]<=> sin(\frac{x}{2}).[cos2x+4.cos^2 (\frac{x}{2}).cosx-5.cos^3x]=0[/TEX]

[TEX]<=> sin(\frac{x}{2}).(4cos^2x+2cosx-5cos^3x-1)=0[/TEX]

Dễ rồi :)
 
Last edited by a moderator:
You must log in or register to reply here.
Top Bottom