Câu trả lời:

1+\(\frac{a+b+c+d}{a}\)=1+\(\frac{a+b+c+d}{b}\)=1+\(\frac{a+b+c+d}{c}\)=1+\(\frac{a+b+c+d}{d}\)Vì \(a+b+c+d\ne\)0 \(\Rightarrow\)a=b=c=d \(\Rightarrow\)