TÍNH :\(12345679\times9\times9=?\)
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đây bài giai nè chưa chăc dung đâu
99+43*9*9*9=
=99+43*9*9*9*1
=9*(99+43+1)
tiếp đó tự làm
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{8.9.10}=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{2.3}\right)+\frac{1}{2}.\left(\frac{1}{2.3}-\frac{1}{3.4}\right)+...+\frac{1}{2}.\left(\frac{1}{8.9}-\frac{1}{9.10}\right)\)
\(=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{8.9}-\frac{1}{9.10}\right)\)
\(\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{9.10}\right)=\frac{1}{2}.\frac{22}{45}=\frac{11}{45}\)
\(P=\dfrac{8^4.3^5-4^6.9^3}{4^6.9^3+4^8.3^5}\)
\(=\dfrac{\left(2^3\right)^4.3^5-\left(2^2\right)^6.\left(3^2\right)^3}{\left(2^2\right)^6.\left(3^2\right)^3+\left(2^2\right)^8.3^5}\)
\(=\dfrac{2^{12}.3^5-2^{12}.3^6}{2^{12}.3^6+2^{16}.3^5}\)
\(=\dfrac{2^{12}\left(3^5-3^6\right)}{2^{12}.2^4\left(3^3+3^5\right)}\)
\(=\dfrac{\left(-3\right)}{8.3^8}\)
\(=\dfrac{-1}{8.3^7}\)
\(P=\dfrac{8^4.3^5-4^6.9^3}{4^6.9^3+4^8.3^5}=\dfrac{2^{12}.3^5-2^{12}.3^6}{2^{12}.3^6+2^{16}.3^5}=\dfrac{2^{12}.3^5\left(1-3\right)}{2^{12}.3^5\left(3+2^4\right)}=\dfrac{-2}{19}\)Nguyễn Thanh Hằng xem lại kết quả đi
\(\dfrac{42x45}{5x7}=\dfrac{7x6x5x9}{5x7}=\dfrac{54}{1}=54\)
\(\dfrac{54x56}{7x9}=\dfrac{6x9x7x8}{7x9}=\dfrac{48}{1}=48\)
18*24+18*128-36-36*5-20*9
=18*24+18*128-18*2-18*2*5-2*10*9
=18*24+18*128-18*2-18*10-18*10
=18*(24+128-2-10-10)
=18*130
=2340
m = 1/3-1/5+1/5-1/7+1/7-1/9+...+1/97-1/99
m = 1/3-1/99=32/99
Sorry chị em ko làm đc câu b vì em mới học lớp 4
k em ha
a) \(M=\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+...+\frac{2}{97\times99}\)
\(\Rightarrow M=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\)
\(\Rightarrow M=\frac{1}{3}-\frac{1}{99}\)
\(\Rightarrow M=\frac{33}{99}-\frac{1}{99}=\frac{32}{99}\)
b) \(N=\frac{3}{5\times7}+\frac{3}{7\times9}+\frac{3}{9\times11}+...+\frac{3}{197\times199}\)
\(\Rightarrow N=3\times\left(\frac{1}{5\times7}+\frac{1}{7\times9}+\frac{1}{9\times11}+...+\frac{1}{197\times199}\right)\)
\(\Rightarrow N=3\times\left[2\times\left(\frac{1}{5\times7}+\frac{1}{7\times9}+\frac{1}{9\times11}+...+\frac{1}{197\times199}\right)\right]\)
\(\Rightarrow N=3\times\left(\frac{2}{5\times7}+\frac{2}{7\times9}+\frac{2}{9\times11}+...+\frac{2}{197\times199}\right)\)
\(\Rightarrow N=3\times\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{197}-\frac{1}{199}\right)\)
\(\Rightarrow N=3\times\left(\frac{1}{5}-\frac{1}{199}\right)\)
\(\Rightarrow N=3\times\frac{194}{995}=\frac{582}{995}\)
----Chúc em học giỏi !----
tính nhanh
357,8 x ( 9+20-19)=3578
15 x 9+15+9-1=15 x 10 +8 =158
\(=999999999\)
= 999999999