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Đặt \(\frac{a}{b}=\frac{c}{d}=k\\ =>\orbr{\begin{cases}a=bk\\c=dk\end{cases}}\)
\(Taco:\left(a+2c\right).\left(b+d\right)=\left(a+c\right).\left(b+2d\right)\)
\(=>\left(bk+2dk\right).\left(b+d\right)=\left(bk+dk\right).\left(b+2d\right)\)
\(=>\frac{bk+2dk}{bk+dk}=\frac{b+2d}{b+d}\)
\(=>\frac{k.\left(b+2d\right)}{k.\left(b+d\right)}=\frac{b+2d}{b+d}\)
\(=>\frac{b+2d}{b+d}=\frac{b+2d}{b+d}\)(ĐPCM)
, Chờ tí mk làm câu b
Ta có :\(\frac{a}{b}=\frac{c}{d}\)
\(\implies\)\(\frac{a}{b}=\frac{c}{d}=\frac{2c}{2d}=\frac{a+2c}{b+2d}\left(1\right)\) \(\implies\) \(\frac{a}{b}=\frac{c}{d}=\frac{a+c}{b+d}\left(2\right)\)
Từ (1);(2)\(\implies\) \(\frac{a+2c}{b+2d}=\frac{a+c}{b+d}\)
\(\implies\) \(\left(a+2c\right).\left(b+d\right)=\left(b+2d\right).\left(a+c\right)\)
ta có a^1005+b^1005 / c^1005+d^1005
=> a^1005/c^1005=b^1005/d^1005
=a/c=b/d=a+b/c+d=(a+b)^2015/(c+d)^1005
ta có \(\frac{a}{b}=\frac{c}{d}\)
=>\(\frac{a}{c}=\frac{b}{d}\)(1)
Từ (1) => \(\frac{a^{1005}}{c^{1005}}=\frac{b^{1005}}{d^{1005}}=\frac{a^{1005}+b^{1005}}{c^{1005}+d^{1005}}\)(2)
Từ (1) => \(\frac{a}{c}=\frac{b}{d}=\frac{a+b}{c+d}\)
=>\(\left(\frac{a}{c}\right)^{1005}=\left(\frac{b}{d}\right)^{1005}=\left(\frac{a+b}{c+d}\right)^{1005}=\frac{\left(a+b\right)^{1005}}{\left(c+d\right)^{1005}}\)(3)
mà \(\left(\frac{a}{c}\right)^{1005}=\frac{a^{1005}}{c^{1005}}\)
từ 2 zà 3 => ghi lại cái cần chứng minh nha ( dpcm)
\(\frac{a}{b}=\frac{c}{d}\Rightarrow\frac{a^{1994}}{b^{1994}}=\frac{c^{1994}}{d^{1994}}\)
áp dụng t/c dãy tỉ số bằng nhau ta có:
\(\frac{a}{b}=\frac{c}{d}=\frac{a+c}{b+d}\)
\(\frac{a^{1994}}{b^{1994}}=\frac{\left(a+c\right)^{1994}}{\left(b+d\right)^{1994}}\)(1)
\(\frac{a^{1994}}{b^{1994}}=\frac{c^{1994}}{d^{1994}}=\frac{a^{1994}+c^{1994}}{b^{1994}+d^{1994}}\)(2)
từ (1) và (2) => \(\frac{a^{1994}+c^{1994}}{b^{1994}+d^{1994}}=\frac{\left(a+c\right)^{1994}}{\left(b+d\right)^{1994}}\left(đpcm\right)\)
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