12 + 32 + 52 + 72 + ........ + 992
= (1 x 1) + (3 x 3) + (5 x 5) + (7 x 7) + ........... + (99 x 99)
= (1 + 3 + 5 + 7 + ....... + 99) x (1 + 3 + 5 + 7 + ............ + 99)
= {[(99 - 1) : 2 + 1] x (99 + 1) : 2]} + {[(99 - 1) : 2 + 1] x (99 + 1) : 2]}
= 2500 x 2500
= 6 250 000
bài 1
A=1*2*3+2*3*4+3*4*5+...+99*100*101
B=1*3*5+3*5*7+...+95*97*99
C=2*4+4*6+..+98*100
D=1*2+3*4+5*6+...+99*100
E=1^2+2^2+3^2+...+100^2
G=1*3+2*4+3*5+4*6+...+99*101+100*102
H=1*2^2+2*3^2+3*4^2+...+99*100^2
I=1*2*3+3*4*5+5*6*7+7*8*9+...+98*99*100
K=1^2+3^2+5^2+...+99^2
a,x/3=2/3+-1/7;b, 2/3*x-4/3=-3/10 c, (2/1*3+2/3*5+2/5*7+ ....+2/97*99) -x=-100/99
a, A= 1+4+4^2+4^3+...+4^100
b, B=7+7^3+7^5+...+7^99
c, C=2+2^3+2^5+2^7+...+2^2009
d, N= 1+2^2+3^2+4^2+5^2+...+99^2
MOI NGUOI GIUP MINH VOI
tính các tổng sau
1) A = 1+7+7^2+7^3+....+7^2007
2) B= 1+4 +4^2+4^3+....+4^100
3) C= 1+3^2 +3^4 +3^6+3^8+....+3^100
4) D= 7+7^3 + 7^5+7^7+7^9+....+7^99
5)E= 2+2^3+2^5+2^7+2^9+....+2^2009
6) B = 1+2^2+2^4+2^6+2^8+....+2^200
7) C= 5+5^3+5^5+5^9+....+5^101
8) D = 13+13^3+13^5+...+13^99
tính nhanh
e)A=1-2+3-4+...+99-100
g)B=1+3-5-7+9+11-...-397-399
h)C=1-2-3+4+5-6-7+..+97-98-99+100
i)D=2^100-2^99-2^98-..-2^2-2-1
Bài tập *
a) 2/1×3 + 2/3×5 + 2/5×7 + ...............+ 2/99×101
b) 5/1×3 + 5/3×5 + 5/ 5×7 + ................ + 5/99×101
Giúp mk bài này nhé mk
TÍNH NHANH
1) S= 1/1*2+1/2*3+1/3*4+...+1/99*100
2) S= 3/1*3+3/3*5+2/5*7+...+2/97*99
3) S= 4/5*7+4/7*9+4/9*11+...+4/59*61
2/1×3+2/3×5+2/5×7+2/7×+11+........+2/99×101
Bài 4: Tính tổng 1) 1 + (-2) + 3 + (-4) + . . . + 19 + (-20) 2) 1 – 2 + 3 – 4 + . . . + 99 – 100 3) 2 – 4 + 6 – 8 + . . . + 48 – 50 4) – 1 + 3 – 5 + 7 - . . . . + 97 – 99 5) 1 + 2 – 3 – 4 + ... + 97 + 98 – 99 - 100
a) 1/2:3+1/3:4+1/4:5+.....+1/99×100
b)2/3:5+2/5:7+2/7×9+....2/97×99
Giúp em với ạ dấu gạch chéo là dấu phần nhé mọi người
