x + 4 = 11
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Ta có : \(\frac{4}{11}.\frac{-2}{9}+\frac{4}{11}\frac{-8}{9}+\frac{4}{11}.\frac{1}{9}\)
= \(\frac{4}{11}.\left(\frac{-2}{9}+\frac{-8}{9}+\frac{1}{9}\right)\)
= \(\frac{4}{11}.\frac{-9}{9}\)
= \(\frac{4}{11}.\left(-1\right)\)
= \(\frac{-4}{11}\)
\(\frac{4}{11}\left(-\frac{2}{9}+-\frac{8}{9}+\frac{1}{9}\right)=\frac{4}{11}1=\frac{4}{11}\)
\(\dfrac{-4}{3}-\dfrac{5}{7}+\dfrac{4}{3}=\left(\dfrac{4}{3}+\dfrac{-4}{3}\right)-\dfrac{5}{7}=0-\dfrac{5}{7}=-\dfrac{5}{7}\)
\(\dfrac{3}{13}\cdot\dfrac{6}{11}+\dfrac{3}{13}\cdot\dfrac{9}{11}-\dfrac{3}{13}\cdot\dfrac{4}{11}=\dfrac{3}{13}\cdot\left(\dfrac{6}{11}+\dfrac{9}{11}-\dfrac{4}{11}\right)=\dfrac{3}{13}\cdot1=\dfrac{3}{13}\)
Đặt : \(A=\dfrac{4}{8\times11}+\dfrac{4}{11\times14}+...+\dfrac{4}{296\times299}\)
\(\dfrac{3\times A}{4}=\dfrac{3}{8\times11}+\dfrac{3}{11\times14}+...+\dfrac{3}{296\times299}\\ =\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}+...+\dfrac{1}{296}-\dfrac{1}{299}\\ =\dfrac{1}{8}-\dfrac{1}{299}\\ A=\left(\dfrac{1}{8}-\dfrac{1}{299}\right)\times4:3=\dfrac{97}{598}\)
Ta đặt
\(A=\dfrac{4}{8\times11}+\dfrac{4}{11\times14}+....+\dfrac{4}{296\times299}\)
\(\dfrac{3}{4}A=\dfrac{3}{8\times11}+\dfrac{3}{11\times14}+....+\dfrac{3}{296\times299}\)
\(\dfrac{3}{4}A=\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}+....+\dfrac{1}{296}-\dfrac{1}{299}\)
\(\dfrac{3}{4}A=\dfrac{1}{8}-\dfrac{1}{299}=\dfrac{291}{2392}\)
\(A=\dfrac{291}{2392}\div\dfrac{3}{4}\)
\(A=\dfrac{97}{598}\)
tính bằng cách thuận tiện nhất
a,4/15 x 7/8 + 4/15 x 2/9
b, 13/29 x 23/11 -13/19 x 8/11 - 13/19 x 4/11
Đặt A=4/9x11+4/11x13+4/13x15+..+4/97x99
A=2x( 2/9x11+2/11x13+...+2/97x99)
A=2x(1/9-1/11+1/11-1/13+...+1/97-1/99)
A=2x(1/9-1/99)
A=2x10/99=20/99
yêu cầu là tính phải ko bn ( lần sau nhớ ghi rõ yêu cầu nhé !)
Đặt A=4/9x11+4/11x13+4/13x15+...+4/97x99
A=2x(2/9x11+2/11x13+...+2/97x99)
A=2x(1/9-1/11+1/11-1/13+...+1/97-1/99)
A=2x(1/9-1/99)
A=2x10/99=20/99
\(=2\left(\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+...+\frac{1}{97}-\frac{1}{99}\right)\)
\(=2\left(\frac{1}{9}-\frac{1}{99}\right)\)
\(=2.\frac{10}{99}\)
\(=\frac{20}{99}\)
\(4.3^{x-1}+2.3^{x+2}=4.3^6+2.3^9\)
\(3^{x-1}.\left(4+2.3^3\right)=3^6.\left(4+2.3^3\right)\)
\(\Leftrightarrow3^{x-1}=3^6\)
\(\Leftrightarrow x-1=6\)
\(\Leftrightarrow x=7\)
Vậy \(x=7\)
\(-\frac{7}{11}.\frac{11}{19}+\frac{-7}{11}.\frac{8}{19}+\frac{-4}{11}=-\frac{7}{11}.\left(\frac{11}{19}+\frac{8}{19}\right)-\frac{4}{11}\)
\(=-\frac{7}{11}.1-\frac{4}{11}=-\frac{7}{11}-\frac{4}{11}\)
\(=-\frac{11}{11}=-1\)
x+4=11
x=11-4
x=7
vậy x=7.
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