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Đúng chưa lại bảo sai đi

x²-xy+y²
=x²-2xy+y²+xy
=(x-y)²+xy

$x^2-y^2+x-y$

$=\left(x^2-y^2\right)+\left(x-y\right)$

$=\left(x+y\right)\left(x-y\right)+\left(x-y\right)$

$=\left(x-y\right)\left(x+y+1\right)$

a/ x4+4x2−5x4+4x2−5

=(x4+4x2+4)−9=(x4+4x2+4)−9

=(x2+2)2−9=(x2+2)2−9
=(x2+2−3)(x2+2+3)=(x2+2−3)(x2+2+3)

=(x2−1)(x2+5)=(x2−1)(x2+5)

b/ 5x3−5x2y−10x2+10xy5x3−5x2y−10x2+10xy

=(5x3−10x2)−(5x2y−10xy)=(5x3−10x2)−(5x2y−10xy)

=5x2(x−2)−5xy(x−2)=5x2(x−2)−5xy(x−2)

=(x−2)(5x2−5xy)=(x−2)(5x2−5xy)

=(x−2)5x(x−y)

Nửa chu vi hìh chữ nhật là :

90 : 2=45 (m)

Cho : ab=23ab=23

⇒a2=b3⇒a2=b3 va a+b=45

Áp dụng tính chất dãy tỉ số bằng nhau ta có : 

a2=b3=a+b2+3=455=9a2=b3=a+b2+3=455=9

Suy ra : a2=18⇒a=9.2=18a2=18⇒a=9.2=18

b3=18⇒b=9.3=27b3=18⇒b=9.3=27

Chiều rong là :18m

Chiều dài là: 27m

Diện tích mảnh đất là:

18.27=486(m2)

Vậy diện tích mảnh đất là 486m2

TL :

486m2

_HT_