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b2 = ac => \(\frac{a}{b}=\frac{b}{c}\)
Áp dụng tính chất của dãy tỉ số bằng nhau ta có: \(\frac{a}{b}=\frac{b}{c}=\frac{a+2007b}{b+2007c}\)
=> \(\left(\frac{a+2007b}{b+2007c}\right)^2=\frac{a+2007b}{b+2007c}.\frac{a+2007b}{b+2007c}=\frac{a}{b}.\frac{b}{c}=\frac{a}{c}\)
Vậy \(\frac{a}{c}=\left(\frac{a+2007b}{b+2007c}\right)^2\)
Ta co:\(b^2=ac\Leftrightarrow\frac{a}{b}=\frac{b}{c}\)
\(=\frac{2007b}{2007c}=\frac{a+2007b}{b+2007c}\)
\(\Rightarrow\left(\frac{a+2007b}{b+2007c}\right)^2=\left(\frac{a}{b}\right)^2=\frac{a}{b}\times\frac{b}{c}=\frac{a}{c}\)
Vậy \(\frac{a}{c}=\left(\frac{a+2007b}{b+2007c}\right)^2\left(đpcm\right)\)
\(b^2=ac\Rightarrow\dfrac{b}{a}=\dfrac{c}{b}\)
Đặt :\(\dfrac{b}{a}=\dfrac{c}{b}=k\Rightarrow b=ak\)
\(c=bk\)
\(\Rightarrow c=akk=ak^2\)
VT\(=\dfrac{a}{c}=\dfrac{a}{ak^2}=\dfrac{1}{k^2}\)
VP \(=\dfrac{\left(a+2007b\right)^2}{\left(b+2007c\right)^2}=\dfrac{\left(a+2007ak\right)^2}{\left(b+2007bk\right)^2}\)
\(=\dfrac{\left[a\left(1+2007k\right)\right]^2}{\left[b\left(1+2007k\right)\right]^2}=\dfrac{a^2\left(1+2007k\right)^2}{b^2\left(1+2007\right)^2}=\dfrac{a^2}{b^2}=\dfrac{a^2}{\left(ak^2\right)}=\dfrac{a^2}{a^2k^2}=\dfrac{1}{k^2}\)
\(\Rightarrow VT=VP\Rightarrow\dfrac{a}{b}=\dfrac{\left(a+2007b\right)^2}{\left(b+2007c\right)^2}\)
Ta có: \(b^2=a.c\Rightarrow\frac{a}{b}=\frac{b}{c}\)
Đặt \(\frac{a}{b}=\frac{b}{c}=k\left(k\in R\right)\)
\(\Rightarrow a=b.k\); \(b=c.k\)
\(\frac{a}{c}=\frac{a.c}{c.c}=\frac{b^2}{c^2}\left(1\right)\)
\(\frac{\left(a+2007b\right)^2}{\left(b+2007c\right)^2}=\frac{\left(b.k+2007b\right)^2}{\left(c.k+2007c\right)^2}=\frac{\left[b\left(k+2007\right)\right]^2}{\left[c.\left(k+2007\right)\right]^2}=\frac{b^2.\left(k+2007\right)^2}{c^2.\left(k+2007\right)^2}=\frac{b^2}{c^2}\left(2\right)\)
Từ \(\left(1\right)\) và \(\left(2\right)\) \(\Rightarrow\frac{a}{c}=\frac{\left(a+2007b\right)^2}{\left(b+2007c\right)^2}\) \(\left(đpcm\right)\)
