\(\dfrac{21}{4}\cdot\dfrac{-11}{4}+\dfrac{21}{4}\cdot\dfrac{1}{2}+\dfrac{21}{4}\cdot\dfrac{-1}{2}\)
\(=\dfrac{21}{4}\cdot\dfrac{-11}{4}\cdot\dfrac{21}{4}+\dfrac{2}{4}+\dfrac{21}{4}\cdot\dfrac{-2}{4}\)
\(=\dfrac{21}{4}\cdot\left(\dfrac{-11}{4}+\dfrac{2}{4}+\dfrac{-2}{4}\right)\)
\(=\dfrac{21}{4}\cdot\dfrac{-11}{4}\)
\(=\dfrac{-231}{16}\)
-3/17+(2/3 +3/17)
-5/21+( -16/21+1)
-4/11 nhân 5/15 nhân 11/-4
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
Câu 3 : Tính nhanh :
a. C = 5 / 11 . 16 + 5 / 16 . 21 + 5 / 21 . 26 + ... + 5 / 61 . 66
b. D = 2 / 1 . 4 + 2 / 4 . 7 + 2 / 7 . 10 + ... + 2 / 97 . 100
1/21 ; 2/21 ; 3/21 ; 4/21 ; 5/21 ; … ; 17/21 ; 18/21 ; 19/21 ; 20/21
1/21 ; 2/21 ; 3/21 ; 4/21 ; 5/21 ; … ; 17/21 ; 18/21 ; 19/21 ; 20/21
1/21+2/21+3/21+4/21+5/21+…+17/21+18/21+19/21+20/21
1/4.12/13+1/4.1/13-12%
*Tìm x bt
a, |2/5:x |=1/4
c,x/24=-1/3-1/8
d, 3/x+3=-7/21
Tính nhanh
A=2/1*5+2/5*9+2/9*13+...+2/97*101+2/101*105
B=4/2*5+4/5*2+4/8*11+...+4/44*47+4/47*50
C=3/1*3*5+3/3*5*7+3/5*7*9+...+3/19*21*23+3/21*23*25
