已知a，b ，c满足a+2c=b，且a⊥c，|a|=1，|c|=2，则|b|=______．
题型：不详难度：来源：
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答案
| a |
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则|
| b |
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则|
| b |
| 17 |
故答案为
| 17 |
举一反三
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①
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②(k
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③
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④
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若平面向量
，
，
两两所成的角相等，|
|=|
|=1，|
|=3，则|++|=（ ）