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Tính giá trị biểu thức : \(\frac{3a-b}{2a+13}-\frac{3b-a}{2b-13}\)biết \(a-b=13\)
Đaq cần gấp, thanks
\(a-b=13\) => \(a=b+13\)
Thay \(a=b+13\) vào biểu thức thì ta sẽ có:
\(\frac{3a-b}{2a+13}-\frac{3b-a}{2b-13}=\frac{3\left(b+13\right)-b}{2\left(b+13\right)+13}-\frac{3b-\left(b+13\right)}{2b-13}\)
\(=\frac{2b+39}{2b+39}-\frac{2b-13}{2b-13}=1-1=0\)
\(=\frac{2a\left(a-b\right)}{2a+13}-\frac{2b-\left(a-b\right)}{2b-13}=\frac{2a+13}{2a+13}-\frac{2b-13}{2b-13}=1-1=0\)
Ta có:\(\frac{3a-b}{2a+15}=\frac{3a-b}{2a+a-b}=\frac{3a-b}{3a-b}=1\)
\(\frac{3b-a}{2b-15}=\frac{3b-a}{2b-\left(a-b\right)}=\frac{3b-a}{3b-a}=1\)
=>P=1+1=2
\(\frac{a}{b}=\frac{-2}{3}\Rightarrow3a=-2b\)
thay vào C ta đc:
\(C=\frac{-2b-2b}{-2b+b}+\frac{-2b+2b}{2\left(-2b\right)-b}\)
=> \(C=\frac{-4b}{-b}+0=4\)
\(a-b=13\Rightarrow a=b+13\)
thay \(a=b+13\) vào biểu thức thì ta có:
\(\frac{3a-b}{2a+13}-\frac{3b-a}{2b-13}=\frac{3\left(b+13\right)-b}{2\left(b+13\right)+13}-\frac{3b-\left(b+13\right)}{2b-13}\)
\(=\frac{2b+39}{2b+39}-\frac{2b-13}{2b-13}=1-1=0\)
\(a,\dfrac{2}{3}.\dfrac{5}{4}-\dfrac{3}{4}.\dfrac{2}{3}=\dfrac{2}{3}.\left(\dfrac{5}{4}-\dfrac{3}{4}\right)=\dfrac{2}{3}.\dfrac{2}{4}=\dfrac{1}{3}\)
\(b,2.\left(\dfrac{-3}{2}\right)-\dfrac{7}{2}=-6.\dfrac{1}{2}-7.\dfrac{1}{2}=\left(-6-7\right).\dfrac{1}{2}=-13.\dfrac{1}{2}=\dfrac{-13}{2}\)
\(c,-\dfrac{3}{4}.5\dfrac{3}{13}-0,75.\dfrac{36}{13}=-\dfrac{3}{4}.\left(\dfrac{68}{13}-\dfrac{36}{13}\right)=-\dfrac{3}{4}.\dfrac{32}{13}=-\dfrac{24}{13}\)
a) \(\dfrac{2}{3}.\dfrac{5}{4}-\dfrac{3}{4}.\dfrac{2}{3}\)
\(=\dfrac{2}{3}.\left(\dfrac{5}{4}-\dfrac{3}{4}\right)\)
\(=\dfrac{2}{3}.\dfrac{2}{4}\)
\(=\dfrac{2}{3}.\dfrac{1}{2}\)
\(=\dfrac{1}{3}\)
b) \(2.\left(\dfrac{-3}{2}\right)^2-\dfrac{7}{2}\)
\(=2.\dfrac{9}{4}-\dfrac{7}{2}\)
\(=\dfrac{9}{2}-\dfrac{7}{2}\)
\(=\dfrac{2}{2}=1\)
c) \(-\dfrac{3}{4}.5\dfrac{3}{13}-0,75.\dfrac{36}{13}\)
\(=-\dfrac{3}{4}.\dfrac{68}{13}-\dfrac{3}{4}.\dfrac{36}{13}\)
\(=\dfrac{3}{4}.\dfrac{-68}{13}-\dfrac{3}{4}.\dfrac{36}{13}\)
\(=\dfrac{3}{4}.\left(\dfrac{-68}{13}-\dfrac{36}{13}\right)\)
\(=\dfrac{3}{4}.\dfrac{-104}{13}\)
\(=\dfrac{3}{4}.\left(-8\right)\)
\(=-6\)
Giá trị của biểu thức \(A\) là \(A=-\frac{3}{8}\).
Ý là 3/8 á bạn
bạn giải rõ ra đc ko, mik tick cho
\(\frac{a}{b}=\frac56\Rightarrow b=\frac{6a}{5}\) (*)
thay (*) vào A ta được:
\(A=\frac{3a-2\cdot\frac{6a}{5}}{2a-3\cdot\frac{6a}{5}}=\frac{3a-2,4a}{2a-3,6a}=\frac{0,6a}{-1,6a}=-\frac38\)
ta có: \(\frac{a}{b}=\frac56\)
=>\(\frac{a}{5}=\frac{b}{6}\)
Đặt \(\frac{a}{5}=\frac{b}{6}=k\)
=>a=5k; b=6k
\(A=\frac{3a-2b}{2a-3b}=\frac{3\cdot5k-2\cdot6k}{2\cdot5k-3\cdot6k}=\frac{15k-12k}{10k-18k}=\frac{3k}{-8k}=-\frac38\)