问题
填空题
如果两圆相切，圆心距为7.5cm，一个圆的半径为4cm，则另一个圆的半径是______cm．
答案
当两圆外切时，
则圆心距等于两圆半径之和，此时另一个圆的半径是7.5-4=3.5（cm）；
当两圆内切时，
圆心距等于两圆半径之差，则另一个圆的半径是7.5+4=11.5（cm）．
故答案为：3.5cm或11.5．
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如果两圆相切，圆心距为7.5cm，一个圆的半径为4cm，则另一个圆的半径是______cm．
当两圆外切时，
则圆心距等于两圆半径之和，此时另一个圆的半径是7.5-4=3.5（cm）；
当两圆内切时，
圆心距等于两圆半径之差，则另一个圆的半径是7.5+4=11.5（cm）．
故答案为：3.5cm或11.5．
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