\(\frac{1}{a}\times\left(a+1\right)...\frac{1}{a}-\frac{1}{a}+1\)
ta có vế trái: \(\frac{1}{a}\times \left(a+1\right)=\frac{1}{a}\times a+\frac{1}{a}\times1=\frac{a}{a}+\frac{1}{a}=1+\frac{1}{a}\)
vế phải: \(\frac{1}{a}-\frac{1}{a}+1=\left(\frac{1}{a}-\frac{1}{a}\right)+1=0+1=1\)
Vì: \(1+\frac{1}{a}>1\)nên \(\frac{1}{a}\times\left(a+1\right)>\frac{1}{a}-\frac{1}{a}+1\)
Vậy \(\frac{1}{a}\times\left(a+1\right)>\frac{1}{a}-\frac{1}{a}+1\)