已知:x-y=7,xy=5,则3xy-7x-7y=?
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已知:x-y=7,xy=5,则3xy-7x-7y=?
已知:x-y=7,xy=5,则3xy-7x-7y=?
已知:x-y=7,xy=5,则3xy-7x-7y=?
(x+y)2=(x-y)2+4xy=7*7+4*5=69
x+y=√69
3xy-7x-7y
=3xy-7(x+y)
=3*5-7*√69
=15-7√69
15-7根号69 根号不会打,能看懂就行
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