Phân tích thành nhân tử ( x+3) (x+2) (x+4) (x+5) -24
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(x+2).(x+3)(x+4)(x+5)-24
=(x+2)(x+5)(x+3)(x+4)-24
=(x2+7x+10)(x2+7x+12)-24
=(x2+7x+11-1)(x2+7x+11+1)-24
Đặt x2+7x+11=a thì
=(a-1)(a+1)-24
=a2-1-24=a2-25=a2-52
=(a+5)(a-5)
=(x2+7x+16)(x2+7x+6)
\(=\left[\left(x+2\right)\left(x+5\right)\right]\left[\left(x+3\right)\left(x+4\right)\right]-24\\ =\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\\ =\left(x^2+7x+11\right)^2-1-24\\ =\left(x^2+7x+11\right)^2-25\\ =\left(x^2+7x+11-5\right)\left(x^2+7x+11+5\right)\\ =\left(x^2+7x+6\right)\left(x^2+7x+16\right)\\ =\left(x+1\right)\left(x+6\right)\left(x^2+7x+16\right)\)
\(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)
\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)
\(=\left(x^2+7x\right)^2+22\left(x^2+7x\right)+96\)
\(=\left(x^2+7x+6\right)\left(x^2+7x+16\right)\)
\(=\left(x+1\right)\left(x+6\right)\left(x^2+7x+16\right)\)
\(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\\ =\left[\left(x+2\right)\left(x+5\right)\right]\left[\left(x+3\right)\left(x+4\right)\right]-24\\ =\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)
Đặt \(x^2+7x+11=y\)
\(\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\\ =\left(y+1\right)\left(y-1\right)-24\\ =y^2-1-24\\ =y^2-25\\ =\left(y-5\right)\left(y+5\right)\\ =\left(x^2+7x+11-5\right)\left(x^2+7x+11+5\right)\\ =\left(x^2+7x+6\right)\left(x^2+7x+16\right)\\ =\left(x+1\right)\left(x+6\right)\left(x^2+7x+16\right)\)
\(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)
\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)
Đặt \(t=x^2+7x+10\) ta có:
\(=t\left(t+2\right)-24=t^2+2t-24\)
\(=t^2-4t+6t-24\)\(=t\left(t-4\right)+6\left(t-4\right)\)
\(=\left(t-4\right)\left(t+6\right)=\left(x^2+7x+10-4\right)\left(x^2+7x+10+6\right)\)
\(=\left(x^2+7x+6\right)\left(x^2+7x+16\right)=\left(x+1\right)\left(x+6\right)\left(x^2+7x+16\right)\)
(x+2)(x+3)(x+4)(x+5)-24
=(x^2+7x+10)(x^2+7x+12)-24
Đặt x^2+7x+10=a
a(a+2)-24
=a^2+2a-24
=(a-4)(a+6)
=(x^2+7x+6)(x^2+7x+16)
=(x+1)(x+6)(x^2+7x+16)
= (x+2)(x+5)(x+3)(x+4)-24
= (x2+7x+10)(x2+7x+12)-24
đặt y=x2+7x+10
ta có biểu thức:
y.(y+2)-24
= y2+2y-24
= y2+6y-4y-24
= y(y+6)-4(y+6)
= (y+6)(y-4)
= (x2+7x+10+6)(x2+7x+10-4)
= (x2+7x+16)(x2+7x+6)
(x + 2)(x + 3)(x + 4)(x + 5) - 24
= (x2 + 3x + 2x + 6)(x2 + 5x + 4x + 20) - 24
= (x2 + 5x + 6)(x2 + 9x + 20) - 24
= x4 + 9x3 + 20x2 + 5x3 + 45x2 + 100x + 6x2 + 54x + 120 - 24
= x4 + 14x3 + 71x2 + 100x + 96
Đặt A = (x^2+5x+4)(x^2+5x+6)-24 và x^2+5x+5=a
Do đó A= (a-1)(a+1)-24
= a^2- 25
= a^2-5^2
=(a-5)(a+5)
= ( x^2+5x+5-5)( x^2+5x+5+5)
= ( x^2+5x)(x^2+5x+10)
Đặt A = (x^2+5x+4)(x^2+5x+6)-24 và x^2+5x+5=a
Do đó A= (a-1)(a+1)-24
= a^2- 25
= a^2-5^2
=(a-5)(a+5)
= ( x^2+5x+5-5)( x^2+5x+5+5)
= ( x^2+5x)(x^2+5x+10)
<=>[(x+2)(x+5)][(x+3)(x+4)]-24=\(\left(x^2+7x+10\right)\left(\left(x^2+7x+12\right)\right)-24\)(1)
đặt x^2+7x+11=t
=> (1)<=> (t-1)(t+1)-24=t^2-1-24=t^2-25=(t-5)(t+5)
<=> \(\left(x^2+7x+11-5\right)\left(x^2+7x+11+5\right)=\left(x^2+7x+6\right)\left(x^2+7x+16\right)=\left(x+1\right)\left(x+6\right)\left(x^2+7x+16\right)\)
(x+2)(x+3)(x+4)(x+5)=24
(x+x+x+x)(2+3+4+5)=24
(x.4)14=24
x.4=24:14
x.4=2
x=2:4
X=1/2
(x+2)(x+5)(x+4)(x+3)-24=(x^2+7x+10)(x^2+7x+12)-24
đặt:x^2+7x+10=t thi x^2+7x+12=t+2
=>t(t+2)-24=t^2+2t-25=t^2+2t+1-25=(t+1)^2-5^2=(t-4)(t+6)
thay t vao suy ra: (x^2+7x+6)(x^2+7x+16)
( x+3) (x+2) (x+4) (x+5) -24
=(x+3)(x+4)(x+2)(x+5)-24
=(x2+7x+12)(x2+7x+10)-24
Đặt t=x2+7x+10 ta được:
(t+2)t-24
=t2+2t-24
=t2+4t-6t-24
=t.(t+4)-6.(t+4)
=(t+4)(t-6)
thay t=x2+7t+10 ta được:
(x2+7x+14)(x2+7+4)
Vậy ( x+3) (x+2) (x+4) (x+5) -24=(x2+7x+14)(x2+7x+4)
song la phai nhuong nhin