\(2\left(x-2\right)\left(x+3\right)-x^2+4=0\)
\(2\left(x^2+3x-2x-6\right)-x^2+4=0\)
\(2x^2+6x-4x-12-x^2+4=0\)
\(x^2+2x-8=0\)
\(x^2+4x-2x-8=0\)
\(x\left(x+4\right)-2\left(x+4\right)=0\)
\(\left(x+4\right)\left(x-2\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x+4=0\rightarrow x=\left(-4\right)\\x-2=0\rightarrow x=2\end{cases}}\)
3/
a/ \(2\left(x+1\right)^2-3\left(x-1\right)^2+\left(x+2\right)\left(5-x\right)\)
\(=2\left(x^2+2x+1\right)-3\left(x^2-2x+1\right)+\left(5x-x^2+10-2x\right)\)
\(=2x^2+4x+2-3x^2+6x-3+5x-x^2+10-2x\)
\(=-2x^2+13x+9\)
b/ \(\left(3x-1\right)^3+\left(3x-1\right)^3-6x^2+9\)
\(=2\left(3x-1\right)^3-6x^2+9\)
\(=2\left(\left(3x\right)^3-3\left(3x\right)^2\cdot1+3\cdot3x\cdot1-1\right)-6x^2+9\)
\(=2\left(27x^3-27x^2+9x-1\right)-6x^2+9\)
\(=54x^3-54x^2+18x-2-6x^2+9\)
\(=54x^3-60x^2+18x+7\)
Số hơi dài, nên dễ tính sai -,- tính mik hay cẩu thả có j sai ibbb ạ
2) 2.(x - 2).(x + 3) - x2 + 4 = 0
<=> x2 + 2x - 8 = 0
<=> (x - 2).(x + 4) = 0
x - 2 = 0 hoặc x + 4 = 0
x = 0 + 2 x = 0 - 4
x = 2 x = -4
=> x = 2 hoặc x = -4
3) a) 2.(x + 1)2 - 3.(x - 1)2 + (x + 2).(5 - x)
= 2.(x2 + 2x + 1) - 3.(x2 - 2x + 1) + (x + 2).(5 - x)
= 2x2 + 4x + 2 - 3x2 + 6x - 3 + (x + 2).(5 - x)
= 2x2 + 4x + 2 - 3x2 + 6x - 3 + 3x - x2 + 10
= (2x2 - 3x2 - x2) + (4x + 6x + 3x) + (2 - 3 + 10)
= -2x2 + 13x + 9
b) (3x - 1)3 + (3x - 1)3 - 6x2 + 9
= 2.(3x - 1)3 - 6x2 + 9
= 2.(27x3 - 27x2 + 9x - 1) - 6x2 + 9
= 54x3 - 54x2 + 18x - 2 - 6x2 + 9
= 54x3 + (-54x2 - 6x2) + 18x + (-2 + 9)
= 54x3 - 60x + 18x + 7
4) a) A = (x - 5).(x + 2) + 3.(x - 2).(x + 2) - (3x - 1)2 + 5x2
A = (x - 5).(x + 2) + 3.(x - 2).(x + 3) - (9x2 - 6x + 1) + 5x2
A = x2 - 3x - 10 + 3x2 - 12 - (9x2 - 6x + 1) + 5x2
A = x2 - 3x - 10 + 3x2 - 12 - 9x2 + 6x - 1 + 5x2
A = (x2 + 3x2 - 9x2 + 5x2) + (-3x + 6x) + (-10 - 12 - 1)
A = 3x - 23 (1)
b) Thay x = 1/2 vào (1), ta có:
A = 3x - 23 = 3.(1/2) - 23
= 3/2 - 23
= -43/2
A khi x = 1/2 là -43/2
