giúp mình với

B

buimaihuong

ta có [TEX]\frac{a+b}{b+b} = \frac{2a}{b}[/TEX]

\Leftrightarrow [TEX]\frac{a+b}{2b} = \frac{2a}{b}[/TEX]

\Leftrightarrow [TEX]b(a+b) = 2a.2b[/TEX]

\Leftrightarrow [TEX]ab + b^2 = 4ab[/TEX]

\Leftrightarrow [TEX]b^2 = 3ab[/TEX] ( b có thể là = -b hoặc b)

\Rightarrow [TEX]b = 3a [/TEX] \Rightarrow [TEX]\frac{a}{b} = \frac{1}{3}[/TEX]
 
V

vodka00

nhớ thanks mình nha

ta có[TEX]\frac{a+b}{b+b}[/TEX]=[TEX]\frac{2a}{b}[/TEX]
[TEX]\Rightarrow[/TEX](a+b).b=(b+b).2a
[TEX]\Rightarrow[/TEX]a.b+b.b=4ab
[TEX]\Rightarrow[/TEX]b.b=3ab
[TEX]\Rightarrow[/TEX]b=3a
[TEX]\Rightarrow[/TEX][TEX]\frac{a}{b}[/TEX]=[TEX]\frac{a}{3a}[/TEX]=[TEX]\frac{1}{3}[/TEX]
 
L

lovelycat_handoi95

[TEX]\blue{\frac{a+b}{2b}=\frac{2a}{b} \\ \Leftrightarrow b^2=3ab \\ \Leftrightarrow b=3a (b \not=0 )\\ \Leftrightarrow \frac{a}{b}=\frac{1}{3}[/TEX]
 
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