Ta có : a) A= 1+ 5+ 52+ 53+........+ 51998
=> 5A = 5+ 52+ 53+........+ 51999
=> 5A - A = 51999 - 1
=> 4A = 51999 - 1
\(\Rightarrow A=\frac{5^{1999}-1}{4}\)
b) Ta có : b) B= 1+ 4+ 42 + ...... + 4n
=> 4B = 4 + 42 + 43 + ...... + 4n + 1
=> 4B - B = 4n + 1 - 1
=> 3B = 4n + 1 - 1
=> \(B=\frac{4^{n+1}-1}{3}\)
A= 1-2+3-4+…+-98+99
Tinh tong sau mot cach hop ly
1/2+1/4+1/16+.....+1/100000
tinh cac tong sau 1 cach hop li
dat dau ngoac 1 cach thich hop nhat de tinh cac tong dai so sau :
a, 834 - 268 +2365 - 1834
b, 13 - 12 + 11 + 10 - 9 +8 -7 - 6 +5 - 4 +3 +2 - 1
dat dau ngoac 1 cach thich hop nhat de tinh cac tong dai so sau :
a, 834 - 268 +2365 - 1834
b, 13 - 12 + 11 + 10 - 9 +8 -7 - 6 +5 - 4 +3 +2 - 1
dat dau ngoac 1 cach thich hop nhat de tinh cac tong dai so sau :
a, 834 - 268 +2365 - 1834
b, 13 - 12 + 11 + 10 - 9 +8 -7 - 6 +5 - 4 +3 +2 - 1
1. tim ket qua cua phep nhan.
A = 33...3 * 99...9
--------- ----------
100so3 100so9
2.cho tap hop cac so tu nhien khong vuot qua 100 chia co 7 du 3
a, hay viet tap hop A = 2 cach
b, tinh tong cac phan tu cu A
c, tinh so chu so dung de viet cac tap hop A
3. nguoi ta danh so trang cua mot quyen sach = day so 1;2;3........quyen sach day 300 trang.hoi
a, tinh so chu so dung de danh so trang sach
b, chu so 659 thuoc trang nao va chu so may
tinh giai tri cac bieu thu sau mot cach hop ly
a , 125 . (-61 ) .(-2)3. ( - 1 )2.n (n thuoc N*)
Tinh tong sau bang cach hop li nhat: (1+3+5+...+99)-(2+4+6+...+100)
1. Cho A = { 1; 2; 3; 4; 5; 6; 7; 8; 9 }. Hay viet tap hop A bang cach chi ra tinh chat dac trung bang 3 cach
2. Tim 3 so tu nhien lien tiep sao cho tong 3 so do la 36
3. Viet tap hop A cac so tu nhien co 3 chu so sao cho tong cac chu so cua moi so la 5
giup minh nhe minh se tickcho ^^ thank you very much !!!
