`a.`\(456-\left(x+23\right)=326\)

`=>x+23=130`

`=>x=107`

`b.(5x-15)(x-4)=0`

\(\Rightarrow\left[{}\begin{matrix}5x-15=0\\x-4=0\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=3\\x=4\end{matrix}\right.\)

`c.89-(x-1)^3=62`

`=>(x-1)^3=27`

`=>(x-1)^3=3^3`

`=>x-1=3`

`=>x=4`

`dx^5-4x^3=0`

`=>x^3(x^2-4)=0`

\(\Rightarrow\left[{}\begin{matrix}x=0\\x^2-4=0\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=0\\x=\pm2\end{matrix}\right.\)

\(R=\dfrac{U}{I}=\dfrac{12}{0,75}=16\left(\Omega\right)\)

\(I=3A\)

\(\Rightarrow U=I.R=3.16=48\left(V\right)\)

\(40:20\) mà cj

`c.`\(100-2\left\{5.2^3:\left[6^2-\left(10+6\right)\right]\right\}\)

\(=100-2\left\{5.8:\left[36-16\right]\right\}\)

\(=100-2\left(40:20\right)\)

\(=100-2.2\)

\(=100-4\)

`=96`

Ta có: \(\widehat{B}_{trong}+\widehat{B}_{ngoài}=180^o\) ( kề bù )

\(\Rightarrow\widehat{B}_{trong}=180^o-50^o=130^o\)

\(\Rightarrow\widehat{C}_{trong}=360^o-130^o-40^o-80^o=110^o\) ( tổng 4 góc của tứ giác )

\(\Rightarrow x=180^o-110^o=70^o\) ( kề bù )

`a.`Diện tích mảnh vườn:

\(36\times12=432\left(m^2\right)\)

`b.` Diện tích trồng cam:

\(432\times\dfrac{2}{3}=288\left(m^2\right)\)

Diện tích đất còn lại:

\(432-288=144\left(m^2\right)\)