Giai phương trình logarit

L

leethuy

de ma ta co [TEX]log_7(x)[/TEX]=[TEX]log_3(sqrt{x}+2)[/TEX]=t
{7}^{t}=x (1)va {3}^{t}= [TEX]sqrt{x}+2[/TEX](2) .
tu (1)ta co [TEX]sqrt{x}[/TEX]={7}^{t/2} sau do ta co pt {7}^{t/2}+2={3}^{t}
sau do chia ca 2 ve cho {7}^{t/2} ta duoc pt moi co dang 1={{\frac{3}{\sqrt{7^t}}}^{t}-{\frac{2}{\sqrt{7^t}} de thay t=2 la no cua he roi suy ra x
 
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