Tính bằng cách hợp lí
1+2+3+4+...+ n
Bài 1: Thực hiện phép tính một cách hợp lí
1, A=(-5/9+5/12):(-10/3)+(-4/9+7/12)
2, B=1/1.4+1/6.2+1/7.10+.....+1/9.100
1: =(-20/36+15/36)*(-3/10)+(-16/36+21/36)
=-5/36*(-3/10)+5/36
=5/36*13/10
=65/360=13/72
2: Bạn xem lại đề nha bạn, dãy số này không có quy luật nào hết luôn á
Bài 1: Bỏ ngoặc rồi tính
1) (15+37) + (52-37-17)
2) (38-42+14) - (25-27-15)
3) (21-32) - (-12+32)
4) (12+21) - (23-21+10)
5) (57-725) - (605-53)
6) (55+45+15) - (15-55+45)
Bài 2: Tính các tổng sau một cách hợp lí
1) (-37) + 14 + 26 + 37
2) (-24) +6 + 10 + 24
3) 15 + 23 + (-25) + (-23)
4) 60 + 33 + (-50) + (-33)
5) (-16) + (-209) + (-14) + 209
6) (-12) + (-13) + 36 + (-11)
Bài 1:
1: =15+37+52-37-17=52-2=50
2: =38-42+14-25+27+15=62-42+29=20+29=49
Bài 1: Bỏ ngoặc rồi tính
3) (21-32) - (-12+32)=21-32-(-12)-32=21-32+12-32=-31
4) (12+21) - (23-21+10)=12+21-23+21-10=21
5) (57-725) - (605-53)=57-725-605+53=-1220
6) (55+45+15) - (15-55+45)=55+45+15-15+55-45=55+55=110
Bài 2: Tính các tổng sau một cách hợp lí
1) (-37) + 14 + 26 + 37=(-37+37)+(14+26)=0+40=40
2) (-24) +6 + 10 + 24=(-24+24)+(6+10)=0+16=16
3) 15 + 23 + (-25) + (-23)=(15-25)+(23-23)=-10+0=-10
4) 60 + 33 + (-50) + (-33)=(60-50)+(33-33)=10+0=10
5) (-16) + (-209) + (-14) + 209=(-16-14)+(-209+209)=-30+0=-30
6) (-12) + (-13) + 36 + (-11)=(-11-12-13)+36=-36+36=0
=15+37+52-37-17 =(37-37)+52+15-17 =0+52+15-17 =67-17 =50
(38 – 42 + 14) – (25 – 27 – 15) =38-42+14-25+27+15 =27 c. -(21 – 32) – (-12 + 32) =-21+32+12-32 =-9 d. -(12 + 21 – 23) - (23 – 21 + 10) =-12-21+23-23+21-10 =-22 e. (57 – 725) – (605 – 53) =57-725-605+53 =-1220 f. (55 + 45 + 15) – (15 – 55 + 45) =55+45+15-15+55-45 =110
V. Hoàn thành các câu sau theo một cách hợp lí
1. My sister has
............................................................................................................................
2. I'd like
............................................................................................................................
3. We feel
............................................................................................................................
4. he likes
............................................................................................................................
5. sometimes they
............................................................................................................................
1 My sister has long black hair
2 I'd like to go out for dinner tonight
3 We feel excited about the school festival
4 He likes watching TV
5 Sometimes they watch TV to 10 p.m
1.a doll
2.some water
3.happy
4.football very much
5.go to shool late
1, My sister has long black hair
2, I'd like to go out for dinner tonight
3, We feel excited about the school festival
4, He likes playing badmintion
5, Sometimes they watch TV to 10 p.m
1) -145.(13 - 57) + 57.(10 -145)
2) 17.(15 - 16) + 16.( 17- 20)
3) -38.(25 - 4) + 25.(-4 + 38 )
4) 23.(145 - 17) - 145.(23 - 6)
5) 24.(15 - 4) + 4.(24 - 15)
6) 199.(15 - 17) - 199.(-17 + 5)
7) -39.(5 - 99) + 99.(10 - 39)
1: \(=-145\cdot13+145\cdot57+57\cdot10-57\cdot145=-1315\)
2: \(=17\cdot15-17\cdot16+16\cdot17-16\cdot20=255-320=-65\)
3: \(=-38\cdot25+38\cdot4-25\cdot4+25\cdot38=13\cdot4=52\)
4: \(=23\cdot145-23\cdot17-145\cdot23+145\cdot6=479\)
5: \(=24\cdot15-24\cdot4+4\cdot24-4\cdot15=360-60=300\)
6: \(=199\left(15-17+17-5\right)=199\cdot10=1990\)
7: \(=-39\cdot5+39\cdot99+99\cdot10-99\cdot39=795\)
1: =−145⋅13+145⋅57+57⋅10−57⋅145=−1315=−145⋅13+145⋅57+57⋅10−57⋅145=−1315
2: =17⋅15−17⋅16+16⋅17−16⋅20=255−320=−65=17⋅15−17⋅16+16⋅17−16⋅20=255−320=−65
3: =−38⋅25+38⋅4−25⋅4+25⋅38=13⋅4=52=−38⋅25+38⋅4−25⋅4+25⋅38=13⋅4=52
4: =23⋅145−23⋅17−145⋅23+145⋅6=479=23⋅145−23⋅17−145⋅23+145⋅6=479
5: =24⋅15−24⋅4+4⋅24−4⋅15=360−60=300=24⋅15−24⋅4+4⋅24−4⋅15=360−60=300
6: =199(15−17+17−5)=199⋅10=1990=199(15−17+17−5)=199⋅10=1990
7: =−39⋅5+39⋅99+99⋅10−99⋅39=795
Bài 1: Tính hợp lí
1. 8 - ( 2014 - 2008 ) + 2014
2. 5679 + ( 1357 - 5679 - 17
3. 1268 - ( 78 + 1268 ) - ( -78 )
4. 13567 - ( 15 - 27 )
5. - 48795 - ( 489 - 48795 ) + 400
6. 15641 - ( 27 + 15641 )
1. 8 - ( 2014 - 2008 ) + 2014
= 8-2014+2008+2014
= (8-2008)+(-2014+2014)
= -2000
2. 5679 + ( 1357 - 5679 - 17
= 5679+1357-5679-17
= 1340
3. 1268 - ( 78 + 1268 ) - ( -78 )
= 1268-78-1268+78
= 0
4. 13567 - ( 15 - 27 )
= 13567+12
= 13579
5. - 48795 - ( 489 - 48795 ) + 400
= -48795-489+48795+400
= (-48795+48795)+(-489+400)
= -89
6. 15641 - ( 27 + 15641 )
= 15641-27-15641
= -27
Tính bằng cách hợp lý 1+2+3+4+...+n
\(S=\dfrac{n\left(n+1\right)}{2}\)
Tính bằng cách hợp lí:
1 + 2 + 3 + 4 +...+ n
Số số hạng là
(n-1):1+1=n(số)
Tổng là
\(\dfrac{\left(n+1\right).n}{2}\)
\(1+2+3+...+n=\dfrac{\left(n+1\right).n}{2}\)
Bạn tính theo công thức này nhé : \(\dfrac{\left(n+1\right)n}{2}\)
Bài 2:Bỏ ngoặc rồi tính hợp lí
1.-(-66)+34+(-73)-27+99
2.54-(45-30+54)-30+5
3.42-56+33-(33-56+42)
4.50-(47+50-18)+(47-18)
5.10-(28-30+4)
6.-(-73)+(44-94+27)+94
1: =66+34-73-27+99=99
2: =54-45+30-54-30+5=-40
3: =42-56+33-33+56-42=0
4: =50-47-50+18+47-18=0
5: =10-28+30-4=2-4+10=12-4=8
\(\text{1.-(-66)+34+(-73)-27+99}.\)
\(=66+34-73-27+99=100-100+99=-99.\)
\(\text{2.54-(45-30+54)-30+5}.\)
\(54-45+30-54-30+5=\left(54-54\right)+\left(-45+5\right)+\left(30-30\right)=-40.\)
\(\text{3.42-56+33-(33-56+42)}.\)
\(=42-56+33-33+56-42=\left(42-42\right)+\left(-56+56\right)+\left(33-33\right)=0.\)
\(\text{4.50-(47+50-18)+(47-18)}.\)
\(=50-47-50+18+47-18=\left(50-50\right)+\left(-47+47\right)+\left(18-18\right)=0.\)
\(\text{5.10-(28-30+4)}.\)
\(=10-28+30-4=10+30-20-8-4=20-12=8.\)
\(\text{6.-(-73)+(44-94+27)+94}.\)
\(=73+44-94+27+94=\left(73+27\right)+\left(-94+94\right)+44=100+44=144.\)
tính tổng sau bằng cách hợp lí : C=4+4 2+4 3+...+ 4 n