5) gọi phân số trên là D
 
Ta có : 
 

Ta có :

\(3a=10b\Rightarrow\dfrac{a}{10}=\dfrac{b}{3}\)

Đặt \(\dfrac{a}{10}=\dfrac{b}{3}=k\)

\(\Rightarrow\left\{{}\begin{matrix}a=10k\\b=3k\end{matrix}\right.\)

\(\Rightarrow\dfrac{16a^2-40ab}{8a^2-24ab}=\dfrac{8a\left(2a-5b\right)}{8a\left(a-3b\right)}=\dfrac{2a-5b}{a-3b}=\dfrac{2.10k-5.3k}{10k-3.3k}=\dfrac{20k-15k}{10k-9k}=\dfrac{5k}{k}=5\)

\(\frac{a}{b}=\frac{10}{3}\)

\(\Rightarrow a=\frac{10}{3}b\)

\(M=\frac{16a^2-40ab}{8a^2-24ab}=\frac{8a\left(2a-5b\right)}{8a\left(a-3b\right)}=\frac{\frac{20}{3}b-5b}{\frac{10}{3}b-3b}=\frac{\frac{5}{3}b}{\frac{1}{3}b}=5\)

Ta có

\(M=\frac{16a^2-40ab}{8a^2-24ab}=\frac{16.\frac{a^2}{b^2}-40.\frac{a}{b}}{8.\frac{a^2}{b^2}-24.\frac{a}{b}}\)

\(=\frac{16.\left(\frac{10}{3}\right)^2-40.\frac{10}{3}}{8.\left(\frac{10}{3}\right)^2-24.\frac{10}{3}}=5\)

?????

67x73 = (70-3)(70+3) = 70² - 3² = 4900 - 9 = 4801.

a) \(16a^2-24ab+9b^2=\left(4a-3b\right)^2.\)

b) \(a^2+4ab+4b^2=\left(a+2b\right)^2\)

TL:

67 x 73 = ( 70 - 3 ) ( 70 + 3 ) = 70² - 3² = 4900 - 9 = 4801

a) \(16a^2\)\(-24ab+9ab=\left(4a-3b\right)^2\)

b) \(a^2\)\(+4ab+4b^2\)\(=\left(a+2b\right)^2\)

~HT~