在四面体ABCD中，若有两组对棱互相垂直，则另一组对棱所成的角为__

在四面体ABCD中，若有两组对棱互相垂直，则另一组对棱所成的角为________．

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在四面体ABCD中，若有两组对棱互相垂直，则另一组对棱所成的角为__

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