Câu hỏi của Linh Vũ

Question

Rut gọn các biểu thức sau

a) (x+y)^2 - (x-y)^2

b) (a+b)^3 + (a-b)^3 - 2a^3

c) 9^8. 2^8 - (18^4 - 1) (18^4+1)

Diệu Huyền · Accepted Answer

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

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

$=x^2+2xy+y^2-x^2+2xy-y^2$

$=4xy$

b, $\left(a+b\right)^3+\left(a-b\right)^3-2a^3$

$=a^3+3a^2b+3ab^2+b^3+\left(a^3-3a^2b+3ab^2-b^3\right)-2a^3$

$=a^3+3a^2b+3ab^2+b^3+a^3-3a^2b+3ab^2-b^3-2a^3$

$=6ab^2$

c, $9^8.2^8-\left(18^4-1\right)\left(18^4+1\right)$

$=\left(9.2\right)^8-\left[\left(18^4\right)^2-1^2\right]$

$=18^8-\left(18^8-1\right)$

$=18^8-18^8+1$

$=1$Câu trả lời: a, $\left(x+y\right)^2-\left(x-y\right)^2$