已知丨a丨=2,丨b丨=4,且丨a+b丨=丨a丨+丨b丨,求a+b-2的值
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|a|=2,|b|=4有四种可能：
1、a = 2,b = 4,此时|a+b| = 6,|a|+|b| = 6,满足题意,所以a+b-2 = 4
2、a = -2,b = -4,此时|a+b| = 6,|a|+|b| = 6,满足题意,所以a+b-2 = -8
3、a = 2,b = -4,此时|a+b| = 2,|a|+|b| = 6,不满足题意,
4、a = -2,b = 4,此时|a+b| = 2,|a|+|b| = 6,不满足题意,
综上,a+b =4或-8
1、a = 2,b = 4,此时|a+b| = 6,|a|+|b| = 6,满足题意,所以a+b-2 = 4
2、a = -2,b = -4,此时|a+b| = 6,|a|+|b| = 6,满足题意,所以a+b-2 = -8
3、a = 2,b = -4,此时|a+b| = 2,|a|+|b| = 6,不满足题意,
4、a = -2,b = 4,此时|a+b| = 2,|a|+|b| = 6,不满足题意,
综上,a+b =4或-8
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