已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值 已知a=13/19,b=-1/4,求已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值已知a=13/19,b=-1/4,求（a+b)²-2(a²-b²)+(b-a

已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值 已知a=13/19,b=-1/4,求已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值已知a=13/19,b=-1/4,求（a+b)²-2(a²-b²)+(b-a
已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值 已知a=13/19,b=-1/4,求
已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值
已知a=13/19,b=-1/4,求（a+b)²-2(a²-b²)+(b-a)²
求证：81^7-27^9-9^13能被45整除

已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值 已知a=13/19,b=-1/4,求已知x=a+b,y=a-b,求（x²+y²）²-（x²-y²）²的值已知a=13/19,b=-1/4,求（a+b)²-2(a²-b²)+(b-a
(x²+y²)²-(x²-y²)²
=(x²+y²+x²-y²)(x²+y²-x²+y²)
=4x²y²
=4(a+b)²(a-b)²
=4(a²-b²)²
=4a^4-8a²b²+4b^4
(a+b)²-2(a²-b²)+(b-a)²
=a²+2ab+b²-2a²+2b²+a²-2ab+b²
=4b²
=4(-1/4)²
=1/4
81^7-27^9-9^13
=9^14-3×9^13-9^13
=9^13(9-3-1)
=5×9^13
=5×9×9^12
=45×9^12
包含因子45,81^7-27^9-9^13能被45整除