Question

Cho S = 3/1x4 + 3/4x7 + 3/7×10 +......+ 3/40×30 + 3/43×46. Hãy chứng tỏ S<1

Ai nhanh mk tích

Answer 1

S=3/1.4+3/4.7+3/7.10+.....+3/40.43+3/43.46

S= 1/1-1/4+1/4-1/7+1/7-1/10+...+1/40-1/43+1/43-1/46

S= 1-1/46

=> S<1

Answer 2

S=3.(1/1-1/4+1/4-1/7+.........+1/40-1/43+1/43-1/46)          

S=3.(1/1-1/46)

S=3.45/46

S=2/43/46

=> 2/43/46>1

=>S>1