当a为何值时,方程组{x-2y=a,4(x-2y)+y=30.的解满足x>y.

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x-2y=a .......14(x-2y)+y=30 .......2由1得x=a+2y代入24（a+2y-2y)+y=30y=30-4a .......3由3代入1得x=2(30-4a)+ax=-7a+60xy-7a+6030-4aa<10