先化简再求值:2(3-5a)平方-5(3a-7)(-3a-7),其中a=-2
问题描述:
先化简再求值:2(3-5a)平方-5(3a-7)(-3a-7),其中a=-2
答
2(3-5a)平方-5(3a-7)(-3a-7)
=50a^2-60a+18-245+45a^2
=95a^2-60a-227
=95x(-2)^2+60x2-227
=380+120-227
=500-227
=273