若|a|=2,|b|=5且|a+b|=a+b求a-b
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|a|=2,|b|=5
有4种情况:
1、a = 2,b = 5,此时|a+b| = 7,a+b = 7.满足题意,所以a - b = 2 - 5 = -3
2、a = -2,b = -5,此时|a+b| = 7,a+b = -7. 不满足题意
3、a = 2,b = -5,此时|a+b| = 3,a+b = -3 不满足题意
4、a = -2,b = 5,此时|a+b| = 3,a+b = 3.满足题意,所以a - b = -2 - 5 = -7
所以a - b = -3或-7
有4种情况:
1、a = 2,b = 5,此时|a+b| = 7,a+b = 7.满足题意,所以a - b = 2 - 5 = -3
2、a = -2,b = -5,此时|a+b| = 7,a+b = -7. 不满足题意
3、a = 2,b = -5,此时|a+b| = 3,a+b = -3 不满足题意
4、a = -2,b = 5,此时|a+b| = 3,a+b = 3.满足题意,所以a - b = -2 - 5 = -7
所以a - b = -3或-7
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