đặt A=1/2×3+1/2×3×4+1/3×4×5+...+1/48×49×50
2A=2.(1/2×3+1/2×3×4+1/3×4×5+...+1/48×49×50)
2A=2/1.2.3+2/2.3.4+......+2/48.49.50
2A=1/2-1/2.3+1/2.3-1/3.4+.....+1/48.49-1/49.50
2A=1/2-1/49.50
A=1/2-1/49.50):2
Tính S/P biết:
S = 1/2 + 1/3 + 1/4 + 1/5 + ... + 1/49 + 1/50
P = 1/49 + 2/48 + 3/47 + ... + 48/2 +49/1
tính các tổng sau
A=1*2+2*3+3*4+4*5+5*6+6*7...+49*50
B=1*50+2*49+3*48+...+49*2+50*1
1/1*2*3*4+1/2*3*4*5+1/3*4*5*6+...+1/47*48*49*
50
Tính A=1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+...+1/(48*49*50)
cho p=1/2+1/3+1/4+…+1/47+1/48+1/49+1/50
q=1/49+2/48+3/49+…47/3+48/2+49/1
tính p/q
1 .2 . 3 + 2 . 3 .4 + 3 . 4. 5 +....... + 48 . 49 .50
S=1/2+1/3+1/4+....+1/49+1/50,P=1/49+2/48+3/47+....+48/2+49/1,hay tim S/P
Tính:
B = 1*2+2*3+3*4+...+2011*2012
C =1*50+2*49+3*48+...+49*2+50*1
D = 4*7+7*10+10*13+...+205*208
E = (2+4+6+8+..+2014)-(3+5+7+9+...+2011)
Tính tổng
B=1/2×3+1/2×3×4+1/3×4×5+...+1/48×49×50
Giúp mk nha mn.......
