Toán Lớp 8: Phân tích đa thức thành nhân tử :
$\ (3x – 2)²(6x – 5)(6x – 3) – 5 $
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Toán Lớp 8: Phân tích đa thức thành nhân tử :
$\ (3x – 2)²(6x – 5)(6x – 3) – 5 $
Comments ( 2 )
(3x-2)^2(6x-5)(6x-3)-5
=(9x^2-12x+4)(36x^2 – 18x – 30x +15)-5
=(9x^2-12x+4)(36x^2 – 48x + 15)-5 (*)
Đặt t=9x^2 – 12x
->4t =36x^2 – 48x
Khi đó :
(*) =(t+4)(4t+15)-5
= 4t^2 + 15t +16t + 60-5
=4t^2+31t + 55
= 4t^2 +11t+20t+55
=t(4t+11)+5(4t+11)
=(4t+11)(t+5)
=(36x^2 – 48x+11)(9x^2-12x+5)
#Rick
(3x-2)^2(6x−5)(6x−3)−5
=(9x^2 – 12x +4)(36x^2 -48x+15)-5
\text{Đặt 9x² – 12x = a, ta có:}
(a+4)(4a+15)-5
=4a^2 +31a+55
= 4a^2 +20a+11a +55
= 4a(a+5)+11(a+5)
=(a+5)(4a+11)
=(9x^2 – 12x +5)(36x^2 – 48x +11)