Question

BT1: tìm x,y:

-4/8 = x/-10 = -7/y

BT2: Chứng tỏ:

A=1/2 mũ 2 + 1/3 mũ 2 + 1/4 mũ 2 +..+ 1/10 mũ 2<1

Answer 1

\(\frac{-4}{8}=\frac{x}{-10}=\frac{-7}{y}\)

Vậy x = -4 . -10 : 8 = 5

=> Y = -10 . 7 : 5 = 14

Câu 2 ( CHỊU) BÓ TAY

Answer 2

\(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{10^2}\)

\(\Rightarrow A< \frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{10}\)

\(\Rightarrow A< \frac{1}{10}+\frac{1}{10}+\frac{1}{10}+...+\frac{1}{10}\) ( 9 số hạng \(\frac{1}{10}\))

\(\Rightarrow A< \frac{9}{10}< 1\)

Vậy \(A< 1\left(đpcm\right)\)