21+31
55/11*16 +55/16*21 +55/21*26 +55/26*31+55/31*36 +55/36*41
Lời giải:
Gọi tổng trên là $A$.
$A=11\times (\frac{5}{11\times 16}+\frac{5}{16\times 21}+\frac{5}{21\times 26}+....+\frac{5}{36\times 41})$
$=11\times (\frac{16-11}{11\times 16}+\frac{21-16}{16\times 21}+\frac{26-21}{21\times 26}+....+\frac{41-36}{36\times 41})$
$=11\times (\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{36}-\frac{1}{41})$
$=11\times (\frac{1}{11}-\frac{1}{41})=1-\frac{11}{41}=\frac{30}{41}$
55/11*16 + 55/16*21 + 55/21*26 + 55/26*31 + 55/31*36 + 55/36*41
\(\dfrac{55}{11}\cdot6+\dfrac{55}{16}\cdot21+\dfrac{55}{21}\cdot26+\dfrac{55}{26}\cdot31+\dfrac{55}{31}\cdot36+\dfrac{55}{36}\cdot41=30+\dfrac{1155}{16}+\dfrac{1430}{21}+\dfrac{1705}{26}+\dfrac{1980}{31}+\dfrac{2255}{36}=\dfrac{12186720}{406224}+\dfrac{29324295}{406224}+\dfrac{27661920}{406224}+\dfrac{26638920}{406224}+\dfrac{25945920}{406224}+\dfrac{25445420}{406224}=\dfrac{147203195}{406224}\)
a = 5/11*16 + 5 / 16 *21 + 5/ 21*26 + 5/ 26 *31 +5/ 31*36 + 5/ 36 *41
\(\frac{5}{11.16}+\frac{5}{16.21}+..+\frac{5}{36.41}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+..+\frac{1}{36}-\frac{1}{41}\)
\(=\frac{1}{11}-\frac{1}{41}\)
= bn tự timnhs nha......................................
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
\(\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{36.41}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{36}-\frac{1}{41}\)
\(=\frac{1}{11}-\frac{1}{41}\)
\(=\frac{30}{451}\)
_Chúc bạn học tốt_
\(A=\frac{5}{11\times16}+\frac{5}{16\times21}+....+\frac{5}{36\times41}.\)
\(A=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{36}-\frac{1}{41}\)
\(A=\frac{1}{11}-\frac{4}{41}=\frac{30}{451}\)
Tinh: 55/11*16+55/16*21+55/21*26+55/26*31+55/31*36+55/36*41
55/11 x 16 + 55/16 x 21 + 55/21 x 26 + 55/26 x 31 + 55/31 x 36 + 55/36 x 41
= 55/11 - 55/16 + 5/16 - 5/21 + 5/21 - 55/26 + 55/26 - 55/31 + 55/31 - 55/36 + 55/36 - 55/41
= 55/11 - 55/41
= 150/41
Mình ko ghi lại đề nha !
= 55 x ( 1/11 x 16 + 1/16 x 21 + 1/21 x 26 + 1/26 x 31 + 1/31 x 36 + 1/36 x 41 )
Vì 1/11 x 16 = 1/1 - 1/11 x 16
=> 1/11 x 21 = 1/231 =1/11 x 16 - 1/16 x 21
....................................................................................
Nếu ta có thể viết :
khúc này viết lại đề bài
= 55 x ( 1/1 - 1/176 + 1/176 -1/336+1/336 - ........................cho đén hết
=55 x ( 1/1 - 1/1476 ) = 55 x 1475/1476 = kết quả tự tính
nhớ
sai rồi kết quả là 30/41 mới đúng
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 hợp lí : b, - 21 nhân 19 - 81 nhân 21 ; d, 31 nhân 72 - 31 nhân 70 - 31 nhâ n 2 : e, 25 nhân( 32 + 47 ) - 32 nhân ( 25 + 47 ) giúp mình với
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
kết quả phép tính : 4/3 x 9/5 - 6/5 + 3 = .....
A.21/5 B.21/15 C.31/5 D.31/15
Tính 101-95 + 91-85 +\ldots + 31-25 + 21-15 + 11-5 =101−95+91−85+…+31−25+21−15+11−5= Câu 10
Bài này khó vãi . Sao ở trong phép tính còn có tiếng anh nữa .
Tính :
( 21/31 + -16/7 ) + ( 44/53 + 10/31 ) + 9/53
\(\left(\dfrac{21}{31}+\dfrac{-16}{7}\right)+\left(\dfrac{44}{53}+\dfrac{10}{31}\right)+\dfrac{9}{53}.\)
\(\dfrac{21}{31}-\dfrac{16}{7}+\dfrac{44}{53}+\dfrac{10}{31}+\dfrac{9}{53}=\left(\dfrac{21}{31}+\dfrac{10}{31}\right)+\left(\dfrac{44}{53}+\dfrac{9}{53}\right)-\dfrac{16}{7}=1+1-\dfrac{16}{7}=\dfrac{-2}{7}.\)