\(\dfrac{20\times25\times7\times8}{75\times8\times12\times14}\)

=   \(\dfrac{4\times5\times25\times7\times8}{3\times25\times8\times3\times4\times2\times7}\)

= \(\dfrac{25\times7\times8\times4\times5}{25\times7\times8\times4\times2\times3\times3}\)

= \(\dfrac{25\times7\times8\times4}{25\times7\times8\times4}\) x \(\dfrac{5}{2\times3\times3}\)

= 1 x \(\dfrac{5}{18}\)

= \(\dfrac{5}{18}\)

\(=\dfrac{5.4.5.5.7.8}{5.3.5.8.7.4}\)

Triệt tiêu những phần giống nhau của cả tử và mẫu ta có: 

\(=\dfrac{5}{3}\)

\(\Leftrightarrow2x^2-x-4x+2-35=0\)

\(\Leftrightarrow2x^2-5x-33=0\)

\(\Leftrightarrow2x^2-11x+6x-33=0\)

\(\Leftrightarrow\left(2x-11\right)\left(x+3\right)=0\)

hay \(x\in\left\{\dfrac{11}{2};-3\right\}\)

\(x+3\frac{1}{2}=24\frac{1}{4}-x\)

\(\Leftrightarrow x+x=24\frac{1}{4}-3\frac{1}{2}\)

\(\Leftrightarrow2x=\frac{94}{4}-\frac{14}{4}\)

\(\Leftrightarrow2x=\frac{90}{4}=\frac{45}{2}\)

\(\Leftrightarrow x=\frac{45}{2}:2\)

\(\Leftrightarrow x=\frac{45}{4}\)

-x-20-(8-2x)=(-12-3)

-x-20-8+2x=-15

x-28=-15

x=13

      Vậy x=13

thank you, trinh thanh cong

\(a.4^{15}.5^{15}=\left(4.5\right)^{15}=20^{15}\)

b . đề sai

4¹⁵:5¹⁵  = (4:5)¹⁵

=0.8¹⁵

d) 5¹².7-5^11.10

=5¹².7-5¹¹⁰