Question

Rút gọn :

A = ( x + y + 3 )² - ( x² + y² + 9 )

B = ( 5x - 2 ) ( 5x + 2 ) - ( 5x - 1)²

C = 100² + 98² + 96² + ......... + 2² - 99² + 97² + 95² + .........+ 1²

Answer 1

Gíup được câu b thoy.

\(B=\left(5x-2\right)\left(5x+2\right)-\left(5x-1\right)^2\\ =25x^2-4-\left(25x^2-10x+1\right)\\ =25x^2-4-25x^2+10x-1\\ =10x-5=5\left(x-1\right)\)

Answer 2

A=\(x^2+y^2+9+2xy+6x+6y+9-x^2-y^2-9\)

A=2xy+6x+6y

B=\(25x^2-4-25x^2+10x-1\)

B=10x-5

C=\(100^2+98^2+...+2^2-\left(99^2+97^2+...+1\right)\)

C=\(100^2-99^2+98^2-97^2+...+4^2-3^2+2^2-1\)

C=\(\left(100-99\right)\left(100+99\right)+...+\left(2-1\right)\left(2+1\right)\)

C=\(199+195+191+...+7+3\)

C=\(\left(199+3\right)\left(\left(199-3\right):4+1\right)=10100\)