2(3-5a)平方-5(3a-7)(3a+7)得多少

问题描述:

2(3-5a)平方-5(3a-7)(3a+7)得多少

20a²-60a+263?

2(3-5a)平方-5(3a-7)(3a+7)
=2(25a²-30a+9)-5(9a²-49)
=50a²-60a+18-45a²+245
=5a²-60a+263