若x,y满足 2x+y=6 x-3y=1 ,求7y(x-3y) 2 -2(3y-x) 3 的值

若x,y满足 2x+y=6 x-3y=1 ,求7y(x-3y) 2 -2(3y-x) 3 的值.
2025-04-29 07:16:39
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回答1:

7y(x-3y) 2 -2(3y-x) 3
=7y(x-3y) 2 +2(x-3y) 3
=(x-3y) 2 [7y+2(x-3y)],
=(x-3y) 2 (2x+y),
2x+y=6
x-3y=1
时,原式=1 2 ×6=6.