\(A = 1.99 + 2.98 + 3.97 + ...+ 97.3 + 98.2 + 99.1\)

\(A=1.99+2.\left(99-1\right)+3.\left(99-2\right)+...+98.\left(99-97\right)+99.\left(99-98\right)\)

\(A=1.99+2.99-1.2+3.99-2.3+98.99-97.98+99.99-98.99\)

\(=\left(1.99+2.99+3.99+...+98.99+99.99\right)-\left(1.2+2.3+3.4+...+97.98+98.99\right)\)

\(=99.\left(1+2+3+...+98+99\right)-\left(1.2+2.3+3.4+...+97.98+98.99\right)\)

\(=99.4950-\left(1.2+2.3+3.4+97.98+98.99\right)\)

Mà \(1.2+2.3+3.4+...97.98+98.99\)

\(=\frac{1}{3}.\left[1.2+2.3.\left(4-1\right)+3.4.\left(5-2\right)+98.99.\left(100-97\right)\right]\)

\(=\frac{1}{3}.98.99.100=323400\)

\(\Rightarrow A=99.4950-323400=166650\)

hic hic mai phải nộp rồi mọi người giúp kim oanh nha oaoa

=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99(99-98)

=99.(1+2+3+4+...+98+99)-(2+2.3+3.4+...+97.98+98.99)

=99.(1+99).99/2-98.99.100/3

=99.50.99-98.33.100

=490050-323400

=166650

=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99(99-98)

=99.(1+2+3+4+...+98+99)-(2+2.3+3.4+...+97.98+98.99)

=99.(1+99).99/2-98.99.100/3

=99.50.99-98.33.100

=490050-323400

=166650

=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99(99-98)

=99.(1+2+3+4+...+98+99)-(2+2.3+3.4+...+97.98+98.99)

=99.(1+99).99/2-98.99.100/3

=99.50.99-98.33.100

=490050-323400

=166650

=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99(99-98)

=99.(1+2+3+4+...+98+99)-(2+2.3+3.4+...+97.98+98.99)

=99.(1+99).99/2-98.99.100/3

=99.50.99-98.33.100

=490050-323400

=166650

166650

các bạn k nhá

bo tay

Ô tô đi với vận tốc 50km/giờ vì :

         100 : 2 = 50

                   đs : 50

Ta có: C = 1.2 + 2.3 + 3.4 + ..... + 98.99

=> 3C = 3.(1.2 + 2.3 + 3.4 + ..... + 98.99)

=> 3C = 1.2.(3 - 0) + 2.3.(4 - 1) + .... + 98.99.(100 - 97)

=> 3C = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ..... + 98.99.100

=> 3C = 98.99.100

=> C = \(C=\frac{98.99.100}{3}=485100\)

Ta có :

C = 1.99 + 2.(99 - 1) + 3.(99 - 2) + ... + 98.(99 - 97) + 99.(99 - 98)

C = 99.(1 + 2 + 3 + ... + 98 + 99) - (2 + 2.3 + 3.4 + ...+97.98 + 98.99)

C = 99.(1 + 99).99/2 - 98.99.100/3

C = 99.50.99 - 98.33.100

C = 490050 - 323400

C = 166650

1.99+2.98+3.97+...+98.2+99.1=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99.(99-98) 

=1.99+2.99-1.2+3.99-2.3+...+98.99-97.98+99.99-98.99 

=(1.99+2.99+3.99+...+98.99+99.99)-(1.2+2.3+3.4+...+98.99) 

=99.(1+2+...+99)-(1.2+2.3+...+98.99)=99.4950-(1.2+2.3+...+98.99)=490050-(1.2+2.3+...+98.99) 

đặt A=1.2+2.3+...+98.99

=>3A=1.2.3+2.3.3+...+98.99.3

=1.2.3+2.3.(4-1)+...+98.99.(100-97) 

=1.2.3-1.2.3+2.3.4-2.3.4+...+97.98.99-97.98.99+98.99.100=98.99.100 

=>A=98.99.100:3=323400

=>1.99+2.98+3.97+...+98.2+99.1=490050-323400=166650 

c/ơn BẢO NAM TRẦN

C=1.99+2.98+3.97+98.2+99.1

C=(1x1x99x99)+(2x98x98x2)+3x97

C=9801+9604+291

C=19405+291

C=19696