\(\left(-\dfrac{1}{3}m^2\right)\left(-24n\right)\left(4mn\right)\)

\(=\left(8nm^2\right)\left(4mn\right)\)

\(=32n^2m^3\)

\(\left(5a\right)\left(a^2b^2\right)\left(-2b\right)\left(-3a\right)\)

\(=\left(5a^35ab^2\right)\left(6ab\right)\)

\(=30a^4b.30a^2b^3\)

Thông cảm mk làm cái này hay sai lắm

\(2a^2b\)

Bài 1: Đặt \(\dfrac{a}{c}=\dfrac{b}{d}=k\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=ck\\b=dk\end{matrix}\right.\)

\(\dfrac{a}{a+c}=\dfrac{ck}{ck+c}=\dfrac{ck}{c\left(k+1\right)}=\dfrac{k}{k+1}\)

\(\dfrac{b}{b+d}=\dfrac{dk}{dk+d}=\dfrac{k}{k+1}\)

Do đó: \(\dfrac{a}{a+c}=\dfrac{b}{b+d}\)

a: \(A=\left(5xy-2xy+4xy\right)+3x-2y-y^2\)

\(=7xy+3x-2y-y^2\)

b: \(B=\left(\dfrac{1}{2}ab^2-\dfrac{7}{8}ab^2-\dfrac{1}{2}ab^2\right)+\left(\dfrac{3}{4}a^2b-\dfrac{3}{8}a^2b\right)\)

\(=\dfrac{-7}{8}ab^2+\dfrac{3}{8}a^2b\)

c: \(C=\left(2a^2b+5a^2b\right)+\left(-8b^2-3b^2\right)+\left(5c^2+4c^2\right)\)

\(=7a^2b-11b^2+9c^2\)

\(A=5xy-y^2-2xy+4xy+3x-2y\)

\(A=-y^2+7xy+3x-2y\)

\(B=\dfrac{1}{2}ab^2-\dfrac{7}{8}ab^2+\dfrac{3}{4}a^2b-\dfrac{3}{8}a^2b-\dfrac{1}{2}ab^2\)

\(B=\dfrac{3}{8}a^2b-\dfrac{7}{8}ab^2\)

\(C=2a^2b-8b^2+5a^2b+5c^2-3b^2+4c^2\)

\(C=7a^2b-11b^2+9c^2\)

\(A=7xy-y^2+3x-2y\)

\(B=\dfrac{3}{8}a^2b-\dfrac{7}{8}ab^2\)
\(C=7a^2b-11b^2+9c^2\)

Bài 1: Đặt \(\dfrac{a}{c}=\dfrac{b}{d}=k\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=ck\\b=dk\end{matrix}\right.\)

\(\dfrac{a}{a+c}=\dfrac{ck}{ck+c}=\dfrac{ck}{c\left(k+1\right)}=\dfrac{k}{k+1}\)

\(\dfrac{b}{b+d}=\dfrac{dk}{dk+d}=\dfrac{k}{k+1}\)

Do đó: \(\dfrac{a}{a+c}=\dfrac{b}{b+d}\)

Từ giả thiết ta có \(\frac{15a-10b}{25}=\frac{6c-15}{9}=\frac{10b-6c}{4}\)

\(=\frac{0}{38}=0\)

(Theo t/c day ti so bang nhau)

Suy ra \(\hept{\begin{cases}15a-10b=0\\6c-15a=0\end{cases}\Rightarrow\hept{\begin{cases}3a-2b=0\\2c-5a=0\end{cases}}}\Rightarrow\hept{\begin{cases}b=\frac{3}{2}a\\c=\frac{5}{2}a\end{cases}}\)

Mà a^2+275=bc Suy ra \(^{a^2+275=\frac{15}{4}a^2\Rightarrow a^2=100\Rightarrow a=\pm10}\)

ĐS: a=10; b=15; c=25 và a=-10; b=-15; c=-25

Sửa chút \(\frac{15a-10b}{25}=\frac{6c-15a}{9}=\frac{10b-6c}{4}\)

Giải:

Ta có: \(\dfrac{a}{b}=\dfrac{-2}{3}\Rightarrow\dfrac{a}{-2}=\dfrac{b}{3}\)

Đặt \(\dfrac{a}{-2}=\dfrac{b}{3}=k\Rightarrow\left\{{}\begin{matrix}a=-2k\\b=3k\end{matrix}\right.\)

\(M=\dfrac{5a+2b}{3a-4b}=\dfrac{-10k+6k}{-6k-12k}=\dfrac{-4k}{-18k}=\dfrac{2}{9}\)

Vậy \(M=\dfrac{2}{9}\)

Từ \(\dfrac{a}{b}=\dfrac{-2}{3}\Rightarrow\dfrac{a}{-2}=\dfrac{b}{3}\)

Đặt \(\dfrac{a}{-2}=\dfrac{b}{3}=k\)

\(\Rightarrow a=-2k\) ; \(b=3k\)

Thay a=-2k và b = 3k vào M , ta có :

\(\dfrac{5.\left(-2\right)k+2.3k}{3.\left(-2\right)k-3.3k}=\dfrac{-10k+6k}{-6k-9k}=\dfrac{k\left(-10+6\right)}{k\left(-6-9\right)}=\dfrac{-4}{-15}=\dfrac{4}{15}\)Vậy...