Đáp án:

Giải thích các bước giải:

 Cho mình xin câu trả lời hay nhất đi ạ

Bài 1:

a) $\dfrac{5^6.20^4}{25^5.4^3}$

$= \dfrac{5^6.(5.4)^4}{(5^2)^5.4^3}$

$= \dfrac{5^6.5^4.4^4}{5^{10}.4^3}$

$= \dfrac{5^{10}.4^4}{5^{10}.4^3}$

$= 4$

b) $3(2x - 3)^2 = 48$

$\Leftrightarrow (2x - 3)^2 = 16$

$\Leftrightarrow |2x - 3| = 4$

$\Leftrightarrow \left[\begin{array}{l}2x - 3 = 4\\2x - 3 = -4\end{array}\right.$

$\Leftrightarrow \left[\begin{array}{l}2x= 7\\2x = -1\end{array}\right.$

$\Leftrightarrow \left[\begin{array}{l}x= \dfrac{7}{2}\\x = -\dfrac{1}{2}\end{array}\right.$

Bài 2:

a) Ta có:

$x//y$

$m\perp x$

$\Rightarrow m\perp y$

$\Rightarrow \widehat{ABD}=90^o$

b) Ta có:

$x//y$

$\Rightarrow \widehat{BDC} + \widehat{C_1} = 180^o$ (trong cùng phía)

$\Rightarrow \widehat{C_1} = 180^o -\widehat{BDC} = 180^o - 57^o = 123^o$

Ta có:

$\widehat{C_2} = \widehat{BDC}$ (so le trong)

$\Rightarrow \widehat{C_2} = 57^o$

$\widehat{C_3} = \widehat{BDC}$ (đồng vị)

$\Rightarrow \widehat{C_3} = 57^o$