toán lớp 8 : phân tích đa thức thành nhân tử

P

pinkylun

a) $x^2+8x+7$

$=x^2+7x+x+7$

$=x(x+7)+(x+7)=(x+1)(x+7)$

b) $=(x-3)(x-2)$

c) $=(x-3)(x+6)$

d)$ =(x-5)(3x-1) $

e) $=(x+1)(x-y)$

f) $=(x+2)^2-y^2=(x+2-y)(x+2+y)$

g) $=16-(x-y)^2=(4-x+y)(4+x-y)$

h) $=(x-1)^2-(2y+1)^2=(x-2y-2)(x+2y)$

g) Đặt $x-y=a;y-z=b;z-x=c=>a+b+c=0$

$=>a+b=-c$

$=>(a+b)^3=-c^3$

$=>a^3+b^3+3ab(a+b)+c^3=0$

$=>a^3+b^3+c^3=-3ab(a+b)=-3ab.(-c)=3abc$

hay $(x-y)^3+(y-z)^3+(z-x)^3=3(x-y)(y-a)(z-x)$



:D
 
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