a={a-2,2a²+5a,12} -3€a求a用十字相乘法解
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![a={a-2,2a²+5a,12} -3€a求a用十字相乘法解](/uploads/image/z/8645745-57-5.jpg?t=a%3D%7Ba-2%2C2a%26%23178%3B%2B5a%2C12%7D+-3%26%238364%3Ba%E6%B1%82a%E7%94%A8%E5%8D%81%E5%AD%97%E7%9B%B8%E4%B9%98%E6%B3%95%E8%A7%A3)
a={a-2,2a²+5a,12} -3€a求a用十字相乘法解
a={a-2,2a²+5a,12} -3€a求a
用十字相乘法解
a={a-2,2a²+5a,12} -3€a求a用十字相乘法解
a=-3/2
∵当a-2=-3时,a=-1,2a²+5a=2-5=-3
集合出现两个-3,所以a-2≠-3
∴2a²+5a=-3
2a²+5a+3=0
(2a+3)(a+1)=0
a=-3/2或a=-1(舍去)
∴a=-3/2