tính nhanh : 33 x 97 + 99
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![](https://rs.olm.vn/images/avt/0.png?1311)
80*33+97*33+34*97+33*17
=33*(80+97+17)+34*97
=33*194+34*97
=33*97*2+34*97
=97*(33*2+34)
=97*100
=9700
tik mik nha bn
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{3}+\frac{13}{15}+\frac{33}{35}+\frac{61}{63}+\frac{97}{99}\)\(+\frac{141}{143}\)
\(=\left(1-\frac{2}{3}\right)+\left(1-\frac{2}{15}\right)\)\(+\left(1-\frac{2}{35}\right)+\left(1-\frac{2}{63}\right)\)\(+\left(1-\frac{2}{99}\right)+\left(1-\frac{2}{143}\right)\)
\(=\left(1+1+1+1+1+1\right)-\)\(\left(\frac{2}{3}+\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}+\frac{2}{143}\right)\)
\(=6-\)\(\left(\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+\frac{2}{9\times11}+\frac{2}{11\times13}\right)\)
\(=6-\)\(\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}\right)\)
\(=6-\left(1-\frac{1}{13}\right)\)
\(=6-\frac{12}{13}\)
\(=\frac{66}{13}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)
Ta có : ( 1 + 2 + 3 + ... + 99)
Số số hạng là: ( 99 - 1 ) : 1 + 1 = 100
Tổng là: ( 99 + 1 ) x 100 : 2 = 5000
=> 5000 x ( 13 - 12 - 1 ) x 15
=> 5000 x 10 x 15
=> 50000 x 15
=> 750000
Ko muốn vt nx :))
![](https://rs.olm.vn/images/avt/0.png?1311)
97 x 99
= 97 x (100 - 1)
= 97 x 100 - 97
= 9700 - 97
= 9603
a) 97x99
=(99-2)x99
=99x99-2x99
=9801-198
=9603.
K nhé các bạn ơi.
![](https://rs.olm.vn/images/avt/0.png?1311)
=[(99-1):2+1]x(99+1)x[45x(3-2-1)]
=(50x100)x(45x0)
=5000x0
=0
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(33\times4+5\times33+33\times3+33-99=33\times4+5\times33+33\times3+33\times1-33\times3\)
\(=33\times\left(4+5+3+1-3\right)=33\times10=330\)
b) \(256+347+453-147-56-253=\left(256-56\right)+\left(347-147\right)+\left(453-253\right)\)
\(=200+200+200=600\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(97.99\\ =97.\left(100-1\right)\\ =9700-97\\ =9603.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
đề :
= 1/100 - (1 / 100.99 +1/99.98 + ...+ 1/3.2 +1/2.1 )
=1/100 - (1 /1.2 +1/ 2.3 +...+ 1/ 98.99 +1 / 99.100)
=1/100 -( 1- 1/ 2 +1/2 -1/3 +...+1/98 -1/99 +1/99 -1/100)
=1/100 - ( 1- 1/100)
=1/100 - 99 /100
= -98/100
= -49 /50
kết quả:3300 nha bn iu
33 x 97 + 99
= 33 x 97 + 33 x 3
= 33 x (97 + 3)
= 33 x 100
= 3300