Tính nhanh
A,1/1×2+1/2×3+1/3×4+1/4×5+……….+1/10×11=
B,1/2×3+1/3×4+………..+1/16×17+1/17×18=
C,2/3×5+2/5×7+2/7×9+2/9×11=
D,3/1×4+3/4×7+3/7×10=
Đ,4/2×6+4/6×10+4/10×14+4/14×18=
AI NHANH TAY MIK CHO 5 SAO NHA
Tính nhanh
A,1/1×2+1/2×3+1/3×4+1/4×5+……….+1/10×11=
B,1/2×3+1/3×4+………..+1/16×17+1/17×18=
C,2/3×5+2/5×7+2/7×9+2/9×11=
D,3/1×4+3/4×7+3/7×10=
Đ,4/2×6+4/6×10+4/10×14+4/14×18=
AI NHANH TAY MIK CHO 5 SAO NHA
Giải thích các bước giải:
`a)`
`1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+……….+1/(10×11)`
`=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……….+1/10-1/11`
`=1/1-1/11`
`=11/11-1/11`
`=10/11`
`b)`
`1/(2×3)+1/(3×4)+………..+1/(16×17)+1/(17×18)`
`=1/2-1/3+1/3-1/4+…………+1/16-1/17+1/17-1/18`
`=1/2-1/18`
`=9/18-1/18`
`=8/18`
`=4/9`
`c)`
`2/(3×5)+2/(5×7)+2/(7×9)+2/(9×11)`
`=1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11`
`=1/3-1/11`
`=11/33-3/33`
`=8/33`
`d)`
`3/(1×4)+3/(4×7)+3/(7×10)`
`=1/1-1/4+1/4-1/7+1/7-1/10`
`=1/1-1/10`
`=10/10-1/10`
`=9/10`
`đ)`
`4/(2×6)+4/(6×10)+4/(10×14)+4/(14×18)`
`=1/2-1/6+1/6-1/10+1/10-1/14+1/14-1/18`
`=1/2-1/18`
`=9/18-1/18`
`=8/18`
`=4/9`
Đáp án:
Ở dưới `downarrow`
Giải thích các bước giải:
`a,1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+……….+1/(10×11)`
`=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……….+1/10-1/11`
`=1/1-1/11`
`=10/11`
`b,1/(2×3)+1/(3×4)+………..+1/(16×17)+1/(17×18)`
`=1/2-1/3+1/3-1/4+…………+1/16-1/17+1/17-1/18`
`=1/2-1/18`
`=4/9`
`c,2/(3×5)+2/(5×7)+2/(7×9)+2/(9×11)`
`=1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11`
`=1/3-1/11`
`=8/33`
`d,3/(1×4)+3/(4×7)+3/(7×10)`
`=1/1-1/4+1/4-1/7+1/7-1/10`
`=1/1-1/10`
`=9/10`
`đ,4/(2×6)+4/(6×10)+4/(10×14)+4/(14×18)`
`=1/2-1/6+1/6-1/10+1/10-1/14+1/14-1/18`
`=1/2-1/18`
`=4/9`