Cho \(\frac{a}{b}=\frac{c}{d}\) CMR:a,\(\frac{\left(a+b\right)^2}{\left(c+d\right)^2}=\frac{a^2+b^2}{c^2+d^2}\)
b,\(\frac{ab}{cd}=\frac{\left(a-b\right)^2}{\left(c-d\right)^2}\)
c,\(\frac{7a^2+5ac}{7a^2-5ac}=\frac{7b^2+5ad}{7b^2-5ad}\)
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