no, they weren't

học tốt

I'm also in grade 6, but i don't know, sorry

In Athens, Greece

A=100+(30:5)

=100+6

=106

B=15+x=450

x=450-15

x=435

Vậy....

A, 100 + ( 30 : 5 )                    B, 15 + x = 450

   =100 +    6                                       x = 450 - 15

   =   106                                             x  =    435

a) 100 + (30 : 5)

= 100 + 6

= 106

b) 15 + x = 450

             x = 450 - 15

             x = 435

-2+4-6+8-...-18+20

=(-2+4)+(-6+8)+...+(-18+20)

=2+2+...+2

=2.5

=10

like mik zứi😎😁

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Bạn cần giúp bài nào ạ? Nếu bạn cần giúp hết, bạn tách các câu ra từng CH riêng nhé, không ai làm hết được tất cả trong 1 CH đâu bạn, mà có làm thì chất lượng cũng chưa được cao. 

\((a+3)^2-(a-1)^2\\ =(a+3-a+1)(a+3+a-1)\\ =4(2a+2)\\ =8(a+1)\\ \)

Vì 8 ⋮ 8 với mọi a ∈ Z.

=> 8(a+1) ⋮ 8 với mọi a ∈ Z.

Vậy ( a + 3 )² - ( a - 1 )² ⋮ 8 với mọi a ∈ Z.