không biết làm

\(205\left[1200-\left(4^2-2.3\right)^3\right]:40\)

\(=205\left[1200-\left(16-6\right)^3\right]:40\)

\(=205\left[1200-10^3\right]:40\)

\(=205\left[1200-1000\right]:40\)

\(=205.200:40\)

\(=205.5\)

\(=1025\)

Ủng hộ nha

205[1200-(4²-2.3)³]:40

=205[1200-10³]:40

=205.200:40

=1025

(1981 x 1982 - 990) : (1980 x 1982 + 992)

=(1980 x 1982+1982 -990) : (1980 x 1982 +992)

=(1980 x 1982 + 992) : ( 1980 x 1982 + 992)

=1

B=[(45.79+45.21)]:90-5^2]:5+2^3                                  B=[(45.79+45.21):90-25]:5+8                                      B=[(45.(79+21):65]:13                                                  B=[(45.100):65]:13                                                        B=[4500:65]:13                                                           B=4500:65:13                                                       

Cau a la ban hay tinh trong dau ngoac don truoc sau do lam nhoac vuong va lam dau ngoac nhon va tinh cac phep tinh con lai

a:100;b:300;c:200;d:3;e:13

205-[1200-(4²-2.3)³]:40

=205-[1200-(16-2.3)³]:40

=205-[1200-(16-6)³]:40

=205-[1200-10³]:40

=205-[1200-1000]:40

=205-200:40

=205-50

=155

Nhớ thk nha bạn

3A = \(1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{39}}\)

 A = \(\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{40}}\)

=> 2A = 3A - A = \(1-\frac{1}{3^{40}}\)=> \(\frac{1-\frac{1}{3^{40}}}{2}=\frac{1}{2}-\frac{1}{3^{40}\cdot2}\)

Mấy câu còn là thì tương tự nhé c

câu b nhân vào \(2^2\)

câu c nhân vào 4

câu a:

3\(^2\) x 5 + 2\(^3\) x 10 - 81 : 3

= 9 x 5 + 8 x 10 - 27

= 45 + 80 - 27

= 125 - 27

= 98

Câu c:

100 : 5\(^2\) + 7 x 3\(^2\)

= 100 : 25 + 7 x 9

= 4 + 63

= 67

Đặt A=1/10+1/40+1/88+1/154+1/238+1/340

A=1/2.5+1/5.8+1/8.11+1/11.14+1/14.17+1/17.20

3A=3/2.5+3/5.8+....+3/17.20

3A=1/2-1/5+1/5-1/8+...+1/17-1/20

3A=1/2-1/20

3A=9/20

2)

Giữ nguyên p/s 1/2^2

Ta có:1/3^2<1/2.3

         1/4^2<1/3.4

        ...............

          1/n^2<1/(n-1).n

=>1/3^2+1/4^2+...+1/n^2<1/2.3+1/3.4+...+1/(n-1).n

=>1/3^2+1/4^2+.....+1/n^2<1/2-1/3+1/3-1/4+.........+1/n-1-1/n

=>1/2^2+1/3^2+.....+1/n^2<1/2^2+1/2-1/n

=>1/2^2+1/3^2+....+1/n^2<3/4-1/n<3/4

3)

2B=2/3.5+2/5.7+....+2/47.49+2/49.51

2B=1/3-1/5+1/5-1/7+.....+1/47-1/49+1/49-1/51

2B=1/3-1/51

2B=16/51

B=16/51:2

B=8/51

A=1+1/2+1/2^2+...+1/2^2010

2A=2+1+1/2+....+1/2^2009

2A-A=(2+1+1/2+...+1/2^2009)-(1+1/2+1/2^2+....+1/2^2010)

A=2-1/2^2010