\(2P=\frac{2}{2.4}+\frac{2}{4.6}+...+\frac{2}{98.100}\)

\(2P=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}+...+\frac{1}{98}-\frac{1}{100}\)

\(2P=\frac{1}{2}-\frac{1}{100}\)

=> P =\(\frac{49}{100}:2=\frac{49}{100}\cdot\frac{1}{2}=\frac{49}{200}\)

\(\frac{2.4+4.6+6.8+...+98.100}{1.2+2.3+3.4+...+49.50}=\frac{4.\left(1.2+2.3+3.4+...+49.50\right)}{1.2+2.3+3.4+...+49.50}=\frac{4}{1}=4\)

(0,5+0,5)÷0,5_0,5×0,5=

Cái này nữa, chữ hơi xấu, thông cảm nha.

1.3+2.4+3.5+4.6+.....+97.99+98.100 

\(=2^2-1+3^2-1+....+99^2-1\)

\(=1^2+2^2+3^2+....+99^2-99\)

\(=\frac{99.100.196}{6}-99\)

\(=328251\)

1.3+2.4+3.5+4.6+.....+97.99+98.100

= 2² - 1 + 3²+...+99² - 1
= 1² + 2² + 3² + 99² - 99
=\(\frac{99.100.199}{6}\) - 99
= 328251

trong sách nâng cao và phát triển 6 đó bạn

A=(1.2)(2.2)+(2.2)(3.2)+...+(50.2)(51.2)

A=1.2.4+2.3.4+...+50.51.4

A=4(1.2+2.3+...+50.51)

M= 1.2+2.3+...+50.51

3M=1.2.3+2.3.(4-1)+...+50.51.(52-49)

=1.2.3+2.3.4-1.2.3+...+50.51.52-49.50.51

= 50.51.52

=132600

=> M=44200

=> A=4M=176800