S1=1+2+3+4+...+n
=>S1=n+...+4+3+2+1
=>2S1=(1+n)+[2+(n-1)]+...+(n+1)
=>2S1=n(n+1)
=>S1=\(\frac{n\left(n+1\right)}{2}\)
1/ Ta có:
S2=2+4+6+8+...+2n
=>S2=2(1+2+3+...+n)
=>S2=2.\(\frac{n\left(n+1\right)}{2}\)
=>S2=n(n+1)
1, tinh tong
a, S = 1+2-3-4+5+6-7-8+...-100+101
b,C= 1.2+2.3+...+99.100
c, 1.2.3+2.3.4+...+98.99.100
2,tim so tu nhien x
a, 2+4+6+... +2x=210
b,x + (x-1)+(x-2)+...+(x-50)=255
c, (x+1)+(x+2)+...+(x+100)=5700
3,
S1 =1+2
S2=3+4+5
S3=6+7+8+9
hay tinh S99= ??
cho 1 dãy số viết theo quy luật 1-2+3-4+5-6
a, tinh tong 50 so dau cua day
b,tinh tong 35 so dau cua day
Cho S1=1+2, S2=2+3+4, S3=3+4+5+6, S4=4+5+6+7+8............ tinh S100
tinh tong
S1 = 1 + (-2) + 3 + (-4) + ... + 2001 + (-2002)
S2 = 1 + (-3) +5 + (-7) + ... + (-1999) + 2001
tinh tong cua 2+4+6...+98+100=
bai1.Tinh tong cua cac so nguyen am tu -1738 den -16
bai2.Tinh tong sau bang 2 cach
A=1+(-2)+3+(-4)+....+99+(-100)
bai1:tinh tong S=1.3+3.5+5.7+...+99.101
bai2 :tinh tong S=1.4+4.7+7.10+...+2017.2020
bai 3: tinh tong N=2.4+4.6+6.8+..+100.102
bai 4: tinh tóng=2.6+6.10+10.14+14.18+...+42.46+50.54
bai 5:tinh tongB=2^2+4^2+6^2+...+100^2
bai 6:C=1^2+3^2+...+100^2
bai7: biet 1^2+2^2+3^2+...+10^2=385 tinh tong 2^2+4^2+6^2+...+20^2
bai 8: tinh tong s=1^2+2^2+3^2+...+99^2
bon ban gop tien mua chung mot chiec may tinh bo tui. ban An gop 1/2 tong so tien cua ba ban khac.ban Bình góp 1/3 tong so tien cua 3 ban khac.ban Cuong gop 1/4 tong so tien cua ba ban khac.con ban Dung gop 15600đ.hoi gia tien cua chiec may tinh bo tui va so tien cua moi nguoi
Cho S=1+32+34+36+..................+398
tinh tong cua S va cmr S chia het cho 10
