求已知x-y=5,xy=6,求(x+y)눀-2x-2y+1的值和3(a-1)눀-75(a+3)눀的值

要过程,要答案
2024-12-24 11:41:49
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回答1:

解:
(x+y)²=x²+y²+2xy=x²+y²-2xy+4xy=(x-y)²+4xy=5²+4×6=49
x+y=±7

(x+y)²-2x-2y+1
=(x+y)²-2(x+y)+1
=49±14+1
=64或36

3(a-1)²-75(a+3)²
=3(a²-2a+1)-75(a²+6a+9)
=3a²-6a+3-75a²-450a-675
=-72a²-456a-672