A= 1+(2-3)+(5-4)+...+(98-99)-100

=1-1+1-1+...+1-1-100

=-100

Ta có: C=1 - 2 - 3 - 4 + 5 - 6 - 7 - 8 + 9 - 10 - 11 - 12 +... + 97 - 98 - 99 - 100

          C= ( 1 - 2 - 3 - 4 ) + ( 5 - 6 - 7 - 8 ) + ( 9 - 10 - 11 - 12 ) + ... + ( 97 - 98 - 99 - 100 )

          C= - 8 + - 16 + -24 + ... + -200

          C= - ( 8 + 16 + 24 +... + 200 )

          C= - \(\frac{\left(8+200\right).25}{2}\)= - 2600

nhớ ấn đúng cho mình nhé!

C=1-2-3-4+5-6-7-8+9-10-11-12+...+97-98-99-100

C=(1-2-3-4)+(5-6-7-8)+(9-10-11-12)+...+(97-98-99-100)

C=(-8)+(-16)+(-24)+...+(-200)           Vì khoảng cánh mỗi số hạng là 8 =>Số các số hạng là:(200-8):8+1=25(số hạng)

C=-(200+8)x25:2

C=-2600

E = 2 − 5 + 8 − 11 + 14 − 17 + ... + 98 − 101 = 2 − 5 + 8 − 11 + 14 − 17 + ... + 98 − 101 = − 3 + − 3 + − 3 + ... + − 3 = − 3.17 = − 51.

A = 2 − 5 + 8 − 11 + 14 − 17 + ... + 98 − 101 = 2 − 5 + 8 − 11 + 14 − 17 + ... + 98 − 101 = − 3 + − 3 + − 3 + ... + − 3 = − 3.17 = − 51.

Bài làm

\(M=\frac{3^2}{2.5}+\frac{3^2}{5.8}+\frac{3^2}{8.11}+...+\frac{3^2}{98.101}\)

\(M=3^2\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{98}-\frac{1}{101}\right)\)

\(M=9\left(\frac{1}{2}-\frac{1}{101}\right)\)

\(M=9.\frac{101-2}{202}\)

\(M=9.\frac{99}{202}\)

\(M=\frac{891}{202}\)

Vậy \(M=\frac{891}{202}\)

\(M=3\left(\frac{3}{2x5}+\frac{3}{5x8}+\frac{3}{8x11}+...+\frac{3}{98.101}\right).\)

\(M=3\left(\frac{5-2}{2.5}+\frac{8-5}{5.8}+\frac{11-8}{8.11}+...+\frac{101-98}{98.101}\right)\)

\(M=3\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{98}-\frac{1}{101}\right)=3\left(\frac{1}{2}-\frac{1}{101}\right)=\frac{3.99}{202}\)

\(A=100+98+96+...+2-97-95-...-1\)

\(A=100+\left(98-98\right)+\left(96-95\right)+...+\left(2-1\right)\)

\(A=100+1+1+...+1\)

\(A=100+1\cdot49\)

\(A=100\cdot49\)

\(A=4900\)

\(B=1+2-3-4+5+6-7-8+9+10-11-12+...-299-300+301+302\)

\(B=1+\left(2-3-4+5\right)+\left(6-7-8+9\right)+...+\left(298-299-300+301\right)+302\)

\(B=1+0+0+...+302\)

\(B=1+302\)

\(B=303\)

�=100+(98−98)+(96−

D = 1 − 2 − 3 + 4 + 5 − 6 − 7 + ... + 97 − 98 − 99 + 100 = 1 − 2 + − 3 + 4 + 5 − 6 + ... + 97 − 98 + − 99 + 100 = − 1 + 1 + − 1 + ... + − 1 + 1 = − 1 + 1 + − 1 + 1 + ... + − 1 + 1 − 1 = 0 + 0 + ... + 0 − 1 = − 1.