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câu 1: 9\(x^2\) + 12\(x\) + 5 =11
(3\(x\))2 + 2.3.\(x\) .2 + 22 + 1 = 11
(3\(x\) + 2)2 = 11 - 1
(3\(x\) + 2)2 = 10
\(\left[{}\begin{matrix}3x+2=\sqrt{10}\\3x+2=-\sqrt{10}\end{matrix}\right.\)
\(\left[{}\begin{matrix}3x=\sqrt{10}-2\\3x=-\sqrt{10}-2\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=\dfrac{\sqrt{10}-2}{3}\\x=\dfrac{-\sqrt{10}-2}{3}\end{matrix}\right.\)
Vậy S = {\(\dfrac{-\sqrt{10}-2}{3}\); \(\dfrac{\sqrt{10}-2}{3}\)}
Câu 2: 6\(x^2\) + 16\(x\) + 12 = 2\(x^2\)
6\(x^2\) + 16\(x\) + 12 - 2\(x^2\) = 0
4\(x^2\) + 16\(x\) + 12 = 0
(2\(x\))2 + 2.2.\(x\).4 + 16 - 4 = 0
(2\(x\) + 4)2 = 4
\(\left[{}\begin{matrix}2x+4=2\\2x+4=-2\end{matrix}\right.\)
\(\left[{}\begin{matrix}2x=-2\\2x=-6\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-1\\x=-3\end{matrix}\right.\)
S = { -3; -1}
3, 16\(x^2\) + 22\(x\) + 11 = 6\(x\) + 5
16\(x^2\) + 22\(x\) - 6\(x\) + 11 - 5 = 0
16\(x^2\) + 16\(x\) + 6 = 0
(4\(x\))2 + 2.4.\(x\) . 2 + 22 + 2 = 0
(4\(x\) + 2)2 + 2 = 0 (1)
Vì (4\(x\)+ 2)2 ≥ 0 ∀ ⇒ (4\(x\) + 2)2 + 2 > 0 ∀ \(x\) vậy (1) Vô nghiệm
S = \(\varnothing\)
Câu 4. 12\(x^2\) + 20\(x\) + 10 = 3\(x^2\) - 4\(x\)
12\(x^2\) + 20\(x\) + 10 - 3\(x^2\) + 4\(x\) = 0
9\(x^2\) + 24\(x\) + 10 = 0
(3\(x\))2 + 2.3.\(x\).4 + 16 - 6 = 0
(3\(x\) + 4)2 = 6
\(\left[{}\begin{matrix}3x+4=\sqrt{6}\\3x+4=-\sqrt{6}\end{matrix}\right.\)
\(\left[{}\begin{matrix}3x=-4+\sqrt{6}\\3x=-4-\sqrt{6}\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=\dfrac{\sqrt{6}-4}{3}\\x=-\dfrac{\sqrt{6}+4}{3}\end{matrix}\right.\)
S = {\(\dfrac{-\sqrt{6}-4}{3}\); \(\dfrac{\sqrt{6}-4}{3}\)}
a) 3x2 .(2x2 - 3yz + x3)= 6x4 - 6x2yz +3x5
b)(24x5 - 12x4 + 6x2 ).6x2 = 144x7 - 72x6 +36x4
a) 3x2 . (2x2 - 3yz + x3)
= 3x2 . 2x2 + 3x2 . (- 3yz) + 3x2 . x3
= 6x4 + (-9x2yz) + 3x5
= 6x4 - 9x2yz + 3x5
\(x^2-5x+6=\left(x-2\right)\left(x-3\right)\)
\(x^2-7x+12=\left(x-2\right)\left(x-5\right)\)
\(x^2+x-12=\left(x-5\right)\left(x+6\right)\)
\(x^2-9x+20=\left(x-4\right)\left(x-5\right)\)
\(=x^2\left(x-6\right)-24\left(x-6\right)=\left(x^2-24\right)\left(x-6\right)\)
\(=x^3+4x^2-10x^2-40x+16x+64\\ =\left(x+4\right)\left(x^2-10x+16\right)\\ =\left(x+4\right)\left(x^2-2x-8x+16\right)\\ =\left(x+4\right)\left(x-2\right)\left(x-8\right)\)
\(\left(24x^5-12x^4+6x^2\right):6x^2\)
\(=\frac{24x^5-12x^4+6x^2}{6x^2}\)
\(=\frac{24x^5}{6x^2}-\frac{12x^4}{6x^2}+\frac{6x^2}{6x^2}\)
\(=4x^3-2x^2+1\)