Question

so sánh A và B

1, A=\(\frac{1}{7.9}\) với B=\(\frac{1}{7}-\frac{1}{9}\)

Answer 1

\(A=\frac{1}{7\cdot9}\)

\(B=\frac{1}{7}-\frac{1}{9}\)

\(2A=\frac{1}{7}-\frac{1}{9}\)

\(\Rightarrow A< B\)

Answer 2

2A = 2 / 7.9

2A = 1/7 - 1/9

=> A < B

Answer 3

A - B = 1/7.9 -1/7 +1/9 =1/9(1/7 -1) -1/7 =1/9 . (-6/7) -1/7 = - (6/ 9.7 +1/7) <0 

nên A<B