Chọn đáp án đúng nhất
A. (−21)+4+(−55)=4+(−21)+(−55)
B. (−21)+4+(−55)=(−55)+4+(−21)
C. (−21)+4+(−55)=4+(−55)+(−21)
D. Cả A, B, C đều đúng
Cho dãy số sau: 0; 1; 2; 3; 5; 8; 13; …Hãy viết tiếp bốn số nữa của dãy số
A. 21; 43; 55; 89.
B.21; 34; 55; 98.
C. 21; 34; 55; 89.
D.21; 34; 57; 87.
C nhé Khi ko tính số 0 trên dãy số trên thì ta có quy luật tổng hai số đằng sau sẽ bằng số ở phía trước (VD 1+2=3;3+2=5;3+5=8;8+5=13;...) mình chúc bạn học tốt nhé
a) 1 và 4/23+(5/21-4/23)+16/21-1/2 b)75%-(5/2+5/3)+(-1/2) ngũ3 c)-3/4.(-55/9).8/11 d)-3/8.6/13+7/13.-3/8+ 1 và 3/8
`a)1 4/23 + ( 5/21-4/23)+16/21-1/2`
`=27/23+5/21-4/23+16/21-1/2`
`=(27/23-4/23)+(5/21+16/21)-1/2`
`=23/23+21/21-1/2`
`=1+1-1/2`
`=2-1/2`
`=4/2-1/2`
`=3/2`
___
`b)75%-(5/2+5/3)+(-1/2)^3`
`=3/4-5/2+5/3+(-1/8)`
`=(3/4-5/2-1/8)+5/3`
`=(6/8-20/8-1/8)+5/3`
`=-15/8+5/3`
`=-45/24+40/24`
`=-5/24`
___
`c)-3/4(-55/9).8/11`
`=-3/4.(-40/9)`
`=-10/3`
__
`d)-3/8 . 6/13 + 7/13 . (-3/8) + 1 3/8`
`= -3/8 . (6/13 + 7/13) + 11/8`
`= -3/8 . 13/13 + 11/8`
`= -3/8 .1 + 11/8`
`= -3/8 + 11/8`
`= 8/8`
`=1`
A=55/11*16+55/16*21+55/21*26+55/26*31+55/31*36+55/36*41
A=55/11.16+55/16.21+...+55/36.41
A=11x(1/11−1/16+1/16−1/21+...+1/36−1/41)
A=11x(1/11−1/41)
A=11x30/451
A=30/41
tính : A=55/11*16 + 55/16*21 + 55/21*26 + 55/26*31 + 55/31*36 + 55/36*41
A=55*[(1/11*16) * 1/5 + (1/16*21) * 1/5 + (1/21*26) * 1/5 + (1/26*31) * 1/5 + (1/31*36) * 1/5 + (1/36*41) * 1/5 ]
= 55* [ (1/11*16) + (1/16*21) + (1/21*26) + (1/26*31) + (1/31*36) + (1/36*41) ] * 1/5
= 55 * [ 1/11-1/16+1/16-1/21+1/21-1/26+1/26-1/31+1/31-1/36+1/36-1/41) * 1/5
= 55 * ( 1/11 - 1/41 ) * 1/5
= 30/41
Tính nhanh: a) (21-1)*(21-2)*(21-3)*...*(21-21)
b) 3*27*8+4*35*6+2*38*12
c) A=(1001+1002+1003+..+2009)*(360*87-360*32-360*55)
giúp mình với
a. (21 - 1) x (21 - 2) x (21 - 3) x ... x (21 - 21)
= 20 x 19 x 18 x ... x 0
= 0
b. 3 x 27 x 8 + 4 x 35 x 6 + 2 x 38 x 12
= (3 x 8) x 27 + (4 x 6) x 35 + (2 x 12) x 38
= 24 x 27 + 24 x 35 + 24 x 38
= 24 x (27 + 35 + 38)
= 24 x100
= 2400
c. A = (1001 + 1002 + 1003 +... + 2009) x (360 x 87 - 360 x 32 - 360 x 55)
= (1001 + 1002 + 1003 + ... + 2009) x [360 x (87 - 32 - 55)]
= (1001 + 1002 + 1003 + ... + 2009) x (360 x 0)
= (1001 + 1002 + 1003 + ... + 2009) x 0
= 0
bỏ dấu ngoặc rồi tính:
1)(38-42+14)-(25-27-15)
2)(12+21)-(23-21+10)
3)(57-725)-(605-53)
4)(55+45+15)-(15-55+45)
\(1,=38-42+14-25+27+15=27\)
\(2,=12+21-23+21-10=21\)
\(3,=57-725-605+53=-1220\)
\(4,=55+45+15-15+55-45=110\)
\(\text{1.(38-42+14)-(25-27-15)}\\ =38-42+14-25+27+15\\ =-4-11+42\\ =27\)
\(\text{2.(12+21)-(23-21+10)}\\ =12+21-23+21-10\\ =33+44-10=67\)
1,=38−42+14−25+27+15=271,=38−42+14−25+27+15=27
2,=12+21−23+21−10=212,=12+21−23+21−10=21
3,=57−725−605+53=−12203,=57−725−605+53=−1220
4,=55+45+15−15+55−45=110
Rút gọn BT
a) x + 21 + (-18) + (-40)
b) -55 - (y + 20) - (-55)
c) -(a - b) + ( a - c -d + b )
CÁC BẠN LÀM NHANH HỘ MÌNH NHÉ; TỪ GIỜ ĐẾN THỨ 4
a) x + 21 + (-18) + (-40)
= x + 21 - 18 - 40
= x - 37
b) -55 - (y + 20) - (-55)
= -55 -y - 20 + 55
= - y - 20
c) -(a - b) + ( a - c -d + b )
= - a + b + a -c - d +b
= 2b - c - d
-55-(y+20)-(-55)=-55-y-20+55=0-y-20=-(y+20)
-(a-b)+(a-c-d+b)
=2b-c-d
55/11*16 +55/16*21 +55/21*26 +55/26*31+55/31*36 +55/36*41
Lời giải:
Gọi tổng trên là $A$.
$A=11\times (\frac{5}{11\times 16}+\frac{5}{16\times 21}+\frac{5}{21\times 26}+....+\frac{5}{36\times 41})$
$=11\times (\frac{16-11}{11\times 16}+\frac{21-16}{16\times 21}+\frac{26-21}{21\times 26}+....+\frac{41-36}{36\times 41})$
$=11\times (\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{36}-\frac{1}{41})$
$=11\times (\frac{1}{11}-\frac{1}{41})=1-\frac{11}{41}=\frac{30}{41}$
Tính:
A=55/11*16+55/16*21+55/21*26+55/26*31+55/31*36+55/36*41
\(A=\frac{55}{11\cdot16}+\frac{55}{16\cdot21}+\frac{55}{21\cdot26}+...+\frac{55}{36\cdot41}\)
\(=\frac{55}{5}\cdot\left(\frac{16-11}{11\cdot16}+\frac{21-16}{16\cdot21}+\frac{26-21}{21\cdot26}+...+\frac{41-36}{36\cdot41}\right)\)
\(=11\cdot\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{26}-\frac{1}{31}+...+\frac{1}{36}-\frac{1}{41}\right)\)
\(=11\cdot\left(\frac{1}{11}-\frac{1}{41}\right)=11\cdot\frac{41-11}{11\cdot41}=\frac{30}{41}\).
55/11*16 + 55/16*21 + 55/21*26 + 55/26*31 + 55/31*36 + 55/36*41
\(\dfrac{55}{11}\cdot6+\dfrac{55}{16}\cdot21+\dfrac{55}{21}\cdot26+\dfrac{55}{26}\cdot31+\dfrac{55}{31}\cdot36+\dfrac{55}{36}\cdot41=30+\dfrac{1155}{16}+\dfrac{1430}{21}+\dfrac{1705}{26}+\dfrac{1980}{31}+\dfrac{2255}{36}=\dfrac{12186720}{406224}+\dfrac{29324295}{406224}+\dfrac{27661920}{406224}+\dfrac{26638920}{406224}+\dfrac{25945920}{406224}+\dfrac{25445420}{406224}=\dfrac{147203195}{406224}\)