Bài 2:
a, Sửa đề:
\(x^2-4=x^2+2x-2x-4=x\left(x+2\right)-2\left(x+2\right)\)
\(=\left(x+2\right)\left(x-2\right)\)
b, \(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)
\(=\left[\left(x+2\right)\left(x+5\right)\right]\left[\left(x+3\right)\left(x+4\right)\right]-24\)
\(=\left(x^2+5x+2x+10\right)\left(x^2+4x+3x+12\right)-24\)
\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)(1)
Đặt \(a=x^2+7x+10\Rightarrow a+2=x^2+7x+12\)
\(\Rightarrow\left(1\right)=a\left(a+2\right)-24=a^2+2a-24\)
\(=a^2-4a+6a-24=a.\left(a-4\right)+6.\left(a-4\right)\)
\(=\left(a-4\right)\left(a+6\right)\)(2)
Vì \(a=x^2+7x+10\) nên
\(\left(2\right)=\left(x^2+7x+10-4\right)\left(x^2+7x+10+6\right)\)
\(=\left(x^2+7x+6\right)\left(x^2+7x+16\right)\)
\(=\left(x^2+x+6x+6\right)\left(x^2+7x+16\right)\)
\(=\left[x.\left(x+1\right)+6.\left(x+1\right)\right]\left(x^2+7x+16\right)\)
\(=\left(x+1\right).\left(x+6\right)\left(x^2+7x+16\right)\)
Chúc bạn học tốt!!!
1,
Dùng định lý Bơ du :
\(f\left(-\dfrac{1}{3}\right)=3\left(-\dfrac{1}{3}\right)^3+10\left(-\dfrac{1}{3}\right)^2+3.\left(-\dfrac{1}{3}\right)+a-5=0\)
\(=>a=5\)
Vậy a = 5 thì A chia hết cho B .
b,
M = \(x^2-4x+4y^2+4y+5\)
= \(\left(x^2-4x+4\right)+\left(4y^2+4y+1\right)+5-\left(1+4\right)\)
\(=\left(x-2\right)^2+\left(2y+1\right)^2+0\)
Vậy GTNN của M = 0
khi x = 2 ; 2y + 1 = 0 => y = 1/2
\(x^2+4=x^2+4x+4-4x\)
\(=\left(x+2\right)^2-\left(2\sqrt{x}\right)^2\)
\(=\left(x-2\sqrt{x}+2\right)\left(x+2\sqrt{x}+2\right)\)
sao lại ra đc :D
