Question

Tìm giá trị của biểu thức : C = \(\frac{7^2}{2.9}+\frac{7^2}{9.16}+\frac{7^2}{16.23}+...+\frac{7^2}{65.72}\)

Answer 1

\(C=\frac{7^2}{2.9}+\frac{7^2}{9.16}+\frac{7^2}{16.23}+....+\frac{7^2}{65.72}\)

\(C=\frac{7^2}{7}\cdot\left(\frac{1}{2}-\frac{1}{9}+\frac{1}{9}-\frac{1}{16}+\frac{1}{16}-\frac{1}{23}+....+\frac{1}{65}-\frac{1}{72}\right)\)

\(C=7\cdot\left(\frac{1}{2}-\frac{1}{72}\right)\)

\(C=7\cdot\frac{35}{72}=\frac{245}{72}\)

Answer 2

C = 49(1/2.9 ... 1/65.72)

C = 49(1/2 - 1/9 +....+ 1/65 - 1/72)

C = 49( 1/2 - 1/72)

C = bạn tự tính nhé

Có j không hiểu thì Ib mình

Answer 3

C=\(7\cdot\left(\frac{7}{2\cdot9}+\frac{7}{9\cdot16}+...+\frac{7}{65\cdot72}\right)\)

=\(7\cdot\left(\frac{1}{2}-\frac{1}{9}+\frac{1}{9}-\frac{1}{16}+...+\frac{1}{65}-\frac{1}{72}\right)\)

=\(7\cdot\left(\frac{1}{2}-\frac{1}{72}\right)\)

=\(\frac{245}{72}\)

Answer 4

\(C=\frac{7^2}{2.9}+\frac{7^2}{9.16}+\frac{7^2}{16.23}+...+\frac{7^2}{65.72}\)

\(=7\left(\frac{7}{2.9}+\frac{7}{9.16}+\frac{7}{16.23}+...+\frac{7}{65.72}\right)\)

\(=7\left(\frac{1}{2}-\frac{1}{9}+\frac{1}{9}-\frac{1}{16}+\frac{1}{16}-\frac{1}{23}+...+\frac{1}{65}-\frac{1}{72}\right)\)

\(=7\left(\frac{1}{2}-\frac{1}{72}\right)\)

\(=\frac{245}{72}\)

Answer 5

\(C=\frac{7^2}{2.9}+\frac{7^2}{9.16}+\frac{7^2}{16.23}+...+\frac{7^2}{65.72}\)

 \(C=7x\left(\frac{1}{2}-\frac{1}{9}+\frac{1}{9}-\frac{1}{16}+\frac{1}{16}-\frac{1}{23}+...+\frac{1}{65}-\frac{1}{72}\right)\)

\(C=7x\left(\frac{1}{2}-\frac{1}{72}\right)=7x\frac{35}{72}\)

\(C=\frac{245}{72}\).