a, (34 196 : 412 + 412 412 412) * 5

= (83 + 412 412 412)* 5

=412 412 495 * 5

= 206 206 2475

Bài 10

ĐKXĐ: \(\left\{{}\begin{matrix}cos\left(1-x\right)\ne0\\2sin2x.cos2x-1\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}cos\left(1-x\right)\ne0\\sin4x\ne1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}1-x\ne\dfrac{\pi}{2}+k\pi\\4x\ne\dfrac{\pi}{2}+k2\pi\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ne1-\dfrac{\pi}{2}-k\pi\\x\ne\dfrac{\pi}{8}+\dfrac{k\pi}{2}\end{matrix}\right.\left(k\in Z\right)\)

Bài 11.

ĐKXĐ: \(\left\{{}\begin{matrix}cos^2x-sin^2x\ne0\\sin2x\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}cos2x\ne0\\sin2x\ne0\end{matrix}\right.\)

\(\Leftrightarrow2x\ne\dfrac{k\pi}{4}\Leftrightarrow x\ne\dfrac{k\pi}{8}\)

Bài 12.

ĐKXĐ: \(\left\{{}\begin{matrix}1-2cos^2x\ne0\\1+tanx\ne0\\cosx\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}cos2x\ne0\\tanx\ne-1\\cosx\ne0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}2x\ne\dfrac{\pi}{2}+k\pi\\x\ne-\dfrac{\pi}{4}+k\pi\\x\ne\dfrac{\pi}{2}+k\pi\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ne\dfrac{\pi}{4}+\dfrac{k\pi}{2}\\x\ne-\dfrac{\pi}{4}+k\pi\\x\ne\dfrac{\pi}{2}+k\pi\end{matrix}\right.\left(k\in Z\right)\)

Bài 10: 

ĐKXĐ của hàm số \(y=\dfrac{tan\left(1-x\right)+2}{2sin2xcos2x-1}\) là: 

\(\left\{{}\begin{matrix}1-x\ne\dfrac{\pi}{2}+k\pi\\2sin2xcos2x-1\ne0\end{matrix}\right.,k\inℤ\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne1-\dfrac{\pi}{2}+k\pi\\sin4x\ne1\end{matrix}\right.,k\inℤ}\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne1-\dfrac{\pi}{2}+k\pi\\4x\ne\dfrac{\pi}{2}+k2\pi\end{matrix}\right.,k\inℤ\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ne1-\dfrac{\pi}{2}+k\pi\\x\ne\dfrac{\pi}{8}+\dfrac{k\pi}{2}\end{matrix}\right.,k\inℤ\)

Lời giải:
a. Chiều dài mảnh vườn là:

$(20+4):2=12$ (m) 

Chiều rộng mảnh vườn: $12-4=8$ (m) 

Diện tích mảnh vườn: $12\times 8=96$ (m²) 

b. Cả vườn đó năm qua đã thu được số kg rau là:

$96:1\times 8=768$ (kg) 

Đổi 768 kg = 7,68 tạ 

a/

\(\overline{ab}x\overline{aba}=\overline{abab}=\overline{ab}x101\)

\(\Rightarrow\overline{aba}=101\Rightarrow a=1;b=0\)

b/

\(99x\overline{ab}=\overline{aabb}=11x\overline{a0b}\)

\(\Rightarrow9x\overline{ab}=\overline{a0b}\)

\(\Rightarrow90xa+9xb=100xa+b\)

\(\Rightarrow8xb=10xa\Rightarrow4xb=5xa\Rightarrow a=\dfrac{4xb}{5}\Rightarrow b=5\)

\(\Rightarrow a=\dfrac{4xb}{5}=\dfrac{4x5}{5}=a\)