Tính nhanh
1-2-3+4+5+7+8+…+1997-1998-1999+2000+2001
1-3+5-7+…+2001-2003+2005
942-2567+2563-1942
Tính nhanh 1-2-3+4+5+7+8+…+1997-1998-1999+2000+2001 1-3+5-7+…+2001-2003+2005 942-2567+2563-1942
By Kennedy
By Kennedy
Tính nhanh
1-2-3+4+5+7+8+…+1997-1998-1999+2000+2001
1-3+5-7+…+2001-2003+2005
942-2567+2563-1942
`a,` Đề sai thì phải? Sửa đề:
`1-2-3+4+5-6-7+8+…+1997-1998-1999+2000`
`=(1-2-3+4)+(5-6-7+8)+…+(1997-1998-1999+2000)`
`=[(1+4)-(2+3)]+[(5+8)-(6+7)]+…+[(1997+2000)-(1998+1999)]`
`=0+0+…+0`
`=0`
`b,1-3+5-7+…+2001-2003+2005`
`=(1-3)+(5-7)+…+(2001-2003)+2005`
`=-2*501+2005`
`=1003`
`c,942-2567+2563-1942`
`=(942-1942)+(-2567+2563)`
`=-1000-4`
`=-1004`
Đáp án:
Giải thích các bước giải:
a. 1-2-3+4+5+7+8+…+1997-1998-1999+2000+2001
=(1-2-3+4)+(5-7-8+9)+…+(1997-1998-1999+2000)+2001
=0+0+…+0+2001
=2001
b. 1−3+5−7+…+2001−2003+2005
=(1−3)+(5−7)+…+(2001−2003)+2005
=−2+(−2)+…+(−2)+2005
=−2 x 1002+2005
=−2004 + 2005
= 1
c. 942-2567+2563-1942
=(942-1942)-(2563-2567)
=-1000-4
=-1004
Chúc bạn học tốt !!!