[(x+2)(x+5)][(x+3)(x+4)] -24 = ( x\(^2\) + 7x + 10)( x\(^2\) + 7x + 12) -24
Đặt : x\(^2\) + 7x + 10 = a ta được:
a * (a+2) - 24 = a\(^2\) + 2a -24 = a\(^2\) + 2a +1 - 5\(^2\) = (a+1)\(^2\) - 5\(^2\)
= (a + 1 -5)( a + 1 +5)
= (a-4)(a+6)
thay a ta được:
(a-4)(a-6) = ( x\(^2\) + 7x + 10 - 4)( x\(^2\) + 7x + 10 - 6)
= (x\(^2\) + 7x + 6)(x\(^2\) + 7x +4)
= (x+1)(x+6)(x\(^2\) + 7x + 4)
NHA!