Nốt câu c
\(C=\frac{97^3+83^3}{180}-97.83\)
\(=\frac{\left(97+83\right)\left(97^2-97.83+83^3\right)}{180}-97.83\)
\(=\frac{180.\left(97^2-97.83+83^2\right)}{180}-97.83\)
\(=97^2-97.83+83^2-97.83\)
\(=\left(97-83\right)^2=14^2=196\)
1.
a) \(2\left(x+3\right)-x^2-3x=0\)
⇔ \(2\left(x+3\right)-x\left(x+3\right)=0\)
⇔ \(\left(x+3\right)\left(2-x\right)=0\)
⇔ \(\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)
b) \(\left(2x+1\right)^2-\left(x-1\right)^2=0\)
⇔ \(\left(2x+1-x+1\right)\left(2x+1+x-1\right)=0\)
⇔ \(3x\left(x+2\right)=0\)
⇔ \(\left[{}\begin{matrix}x=0\\x=-2\end{matrix}\right.\)
c) \(x^2-4x+3=0\)
⇔ \(x\left(x-1\right)-3\left(x-1\right)=0\)
⇔ \(\left(x-1\right)\left(x-3\right)=0\)
⇔ \(\left[{}\begin{matrix}x=1\\x=3\end{matrix}\right.\)
2, a) \(B=\left(2x+3\right)\left(4x^2-6x+9\right)-2\left(4x^3-1\right)-2x\)
⇔ \(B=8x^3+27-8x^3+2-2x=29-2x\)
Tại x = 3
Thì B = 29 - 6 = 23
