\(\left(36:0,25-72x2\right)x\left(1+2+3+...+100\right)\)

\(=\left(144-144\right)x\left(1+2+3+...+100\right)\)

\(=0x\left(1+2+3+...+100\right)\)

\(=0\)

Ta có 

\(\frac{1}{2^2}<\frac{1}{1.2}\)

\(\frac{1}{3^2}<\frac{1}{2.3}\)

\(\frac{1}{4^2}<\frac{1}{3.4}\)

......

\(\frac{1}{100^2}<\frac{1}{99.100}\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}<\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}<1\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}<\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}<1\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}<1-\frac{1}{100}<1\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}<\frac{99}{100}<1\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+....+\frac{1}{100^2}<1\)

\(\frac{1}{2^2}=\frac{1}{2.2}<\frac{1}{1.2};\frac{1}{3^2}=\frac{1}{3.3}<\frac{1}{2.3};...;\frac{1}{100^2}=\frac{1}{100.100}<\frac{1}{99.100}\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+..+\frac{1}{100^2}<\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{99.100}=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+..+\frac{1}{99}-\frac{1}{100}\)

\(\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+..+\frac{1}{100^2}<1-\frac{1}{100}<1\Rightarrow\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{100^2}<1\left(đpcm\right)\)

bài này mà lp 8 cái j

mình chỉ biết tính chậm thôi

( x + 1 ) + ( x + 2 ) + ( x + 3 ) +... + ( x + 100 ) = 5750 

( x + x + x + ... + x ) + ( 1 + 2 + 3 + ... + 100 ) = 5750

( x . 100 ) + ( 1 . 100 ) . 100 : 2 = 5750 

( x . 100 ) + 5050 = 5750

x . 100 = 5750 - 5050

x . 100 = 700 

x = 700 : 100 

x = 7 

Vậy x = 7 

viết sai đề rồi em ơi 

199 + ( 100 - 50 ) x 2 = 199 + 50 x 2

                                  = 199 + 100

                                  = 299

bằng 299 nha bn

\(\frac{1}{\sqrt{a}+\sqrt{a+1}}=\frac{\sqrt{a+1}-\sqrt{a}}{\left(\sqrt{a}+\sqrt{a+1}\right)\left(\sqrt{a+1}-\sqrt{a}\right)}=\frac{\sqrt{a+1}-\sqrt{a}}{a+1-a}=\sqrt{a+1}-\sqrt{a}\Rightarrow\frac{1}{1+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+.......+\frac{1}{\sqrt{99}+\sqrt{100}}=-1+\sqrt{2}-\sqrt{2}+\sqrt{3}-......-\sqrt{99}+\sqrt{100}=10-1=9\)