\(\frac{1}{1+2}+\frac{1}{1+2+3}+...+\frac{1}{1+2+...+10}\)
=\(\frac{1}{3}+\frac{1}{6}+...+\frac{1}{55}\)
=\(2\cdot\left(\frac{1}{6}+\frac{1}{12}+...+\frac{1}{110}\right)\)
=\(2\cdot\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{10}-\frac{1}{11}\right)=2\cdot\left(\frac{1}{2}-\frac{1}{11}\right)=\frac{9}{11}\)
tính (1/2+1/3+...+1/10)+(2/3+2/4+...+2/10)+(3/4+3/5+...+3/10)+...+(8/9+8/10)+9/10
1+1/2+1/3+1/4+....+1/8+1/9+1/10
1/1*10+1/2*9+1/3*8+......+1/8*3+1/2*9+1/10*1
tính
a) 1 1/6 + 1 4/9 =
b) 2 3/4 : 1 3/19 =
c) ( 4 1/5 - 2 3/10 ) x 2 1/2 =
d) 3 3/7 : 6 1/2 x 1 2/5 =
B=1/1*2*3*4 + 1/2*3*4*5 + 1/3*4*5*6 + 1/8*9*10*11 + 1/9*10*11*12 = ?
1+1+1+1+2+2+2+3+3+3+3+4+4+4+4+5+5+5+5+6+6+6+6+7+7+7+7+8+8+8+8+9+9+9+9+10=
Tính
a) 4/3*7 + 4/7*11 + 4/11*15 + 4/15*19 + 4/19*23 + 4/23*27
b) 1/2*3 + 1/3*4 + 1/4*5 + 1/5*6 +1/6*7
c) 2/3*5 + 2/5*7 + 2/7*9 + 2/9*11 + 2/11*13 + 2/1*2 + 2/2*3 + 2/3*4 + 2/8*9 + 2/9*10
1/1+2+1/1+2+3+1/1+2+3+4.......+1/1=2+3+4+5+6+7+8+9+10
tính nhanh
C = 5 9/10 : 3/2 - ( 2 1/3 x 4 1/2 - 2 x 2 1/3 ) : 7/4
5 9/10 ; 2 1/3 ; 4 1/2 ; 2 1/3 là hỗn sốGiúp mk nha , ai nhanh mk tick cho . Thông cảm mk ko viết được hôn số . Ahihi
