Bài 1:
\(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)
\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)
Đặt x2 + 7x + 10 = t
\(\Rightarrow t\left(t+2\right)-24=t^2+2t-24=\left(t-4\right)\left(t-6\right)\)
\(=\left(x^2+7x+10-4\right)\left(x^2+7x+10-6\right)\)
\(=\left(x^2+7x+6\right)\left(x^2+7x+4\right)\)
Sai thì chịu!
Nhầm tí!
Bài 1:
Đặt x2 +7x + 10 = t
\(\Rightarrow t\left(t+2\right)-24=t^2+2t-24=\left(t-4\right)\left(t+6\right)\)
\(=\left(x^2+7x+6\right)\left(x^2+7x+16\right)\)
Bài 2:
\(A=-\left(x^2-4x+5\right)=-\left(x^2-4x+4+1\right)\)
\(=-\left(x-2\right)^2-1\le-1\)
Đẳng thức xảy ra khi x = 2
\(B=-\left(x^2+6x+9-9\right)=-\left(x+3\right)^2+9\le9\)
Đẳng thức xảy ra khi x = -3
