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\(a,A=\frac{-251489}{15750}\)
b,\(B=\frac{47}{12}\)
\(c,C=\frac{11}{25}\)
\(d,D=\frac{10}{39}\)
\(A=\frac{2-\frac{2}{19}+\frac{2}{43}-\frac{2}{1995}}{3-\frac{3}{19}+\frac{3}{43}-\frac{3}{1995}}:\frac{4-\frac{4}{29}+\frac{4}{41}-\frac{4}{2941}}{5-\frac{5}{29}+\frac{5}{41}-\frac{5}{2941}}\)
\(\Rightarrow A=\frac{2\left(1-\frac{1}{19}+\frac{1}{43}-\frac{1}{1995}\right)}{3\left(1-\frac{1}{19}+\frac{1}{43}-\frac{1}{1995}\right)}:\frac{4\left(1-\frac{1}{29}+\frac{1}{41}-\frac{1}{2941}\right)}{5\left(1-\frac{1}{29}+\frac{1}{41}-\frac{1}{2941}\right)}\)
\(\Rightarrow A=\frac{2}{3}:\frac{4}{5}\)
\(\Rightarrow A=\frac{2}{3}.\frac{5}{4}\)
\(\Rightarrow A=\frac{10}{12}=\frac{5}{6}\)
\(2^1+2^2+2^3+...+2^{10}+2^{11}+2^{12}\)
\(=\left(2.1+2.2+2.2^2\right)+...+\left(2^{10}.1+2^{10}.2+2^{10}.2^2\right)\)
\(=2.\left(1+2+4\right)+...+2^{10}.\left(1+2+4\right)\)
\(=2.7+...+2^{10}.7\)
\(=7.\left(2+...+2^{10}⋮7\right)\RightarrowĐPCM\)
Đặt A=2^1+...+2^12
=>A=(2^1+2^2+2^3)+(2^4+2^5+2^6)+...+(2^10+2^11+2^12)
=>A=2(1+2+4)+2^4(1+2+4)+...+2^10(1+2+4)
=>A=7(2+2^4+...+2^10) chia hết cho 7
Đúng ko biết !
a ) 13/20
B)
C..........................................................
minh dang tính
6) \(2\left(x-8\right)=2^2\)
\(\Rightarrow x-8=2^2:2\)
\(\Rightarrow x-8=2\)
\(\Rightarrow x=2+8\)
\(\Rightarrow x=10\)
tíc mình nha
5) 14 chia hết cho 2x+3
=>2x+3 thuộc ước 14
mà Ư(14)={1,2,7,14}
ta có
| 2x+3 | 1 | 2 | 3 | 14 |
| x | X | X | 0 | X |
vậy x=0
\(-\dfrac{1}{2}-\dfrac{2}{3}+\left(\dfrac{-3}{4}\right)+\dfrac{2}{3}\\ =-\dfrac{1}{2}-\dfrac{3}{4}-\left(\dfrac{2}{3}-\dfrac{2}{3}\right)\\ =-\dfrac{1}{2}-\dfrac{3}{4}=-\left(\dfrac{1}{2}+\dfrac{3}{4}\right)=-\dfrac{5}{4}\)
\(-\dfrac{4}{3}-\dfrac{3}{8}+\dfrac{7}{3}-\dfrac{3}{2}\\ =-\left(\dfrac{4}{3}-\dfrac{7}{3}\right)-\dfrac{3}{8}-\dfrac{3}{2}\\ =-\left(-\dfrac{3}{3}\right)-\dfrac{3}{8}-\dfrac{3}{2}\\ =1-\dfrac{3}{8}-\dfrac{3}{2}\\ =\dfrac{8}{8}-\dfrac{3}{8}-\dfrac{12}{8}=-\dfrac{7}{8}\)
b) \(-\dfrac{1}{2}-\dfrac{2}{3}+\dfrac{-3}{4}+\dfrac{2}{3}\)
\(=\left(-\dfrac{1}{2}+\dfrac{-3}{4}\right)+\left(-\dfrac{2}{3}+\dfrac{2}{3}\right)\)
\(=\left(\dfrac{-2}{4}+\dfrac{-3}{4}\right)+0\)
\(=\dfrac{-5}{4}\)
c) \(\dfrac{-4}{3}-\dfrac{3}{8}+\dfrac{7}{3}-\dfrac{3}{2}\)
\(=\left(\dfrac{-4}{3}+\dfrac{7}{3}\right)+\left(-\dfrac{3}{8}-\dfrac{3}{2}\right)\)
\(=\dfrac{3}{3}+\left(-\dfrac{3}{8}-\dfrac{12}{8}\right)\)
\(=1-\dfrac{15}{8}\)
\(=-\dfrac{7}{8}\)