当a=3时求多项式(7a²-4a)-(5a²-a-1)+(2-a²+4a)的值
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![当a=3时求多项式(7a²-4a)-(5a²-a-1)+(2-a²+4a)的值](/uploads/image/z/1107655-7-5.jpg?t=%E5%BD%93a%3D3%E6%97%B6%E6%B1%82%E5%A4%9A%E9%A1%B9%E5%BC%8F%EF%BC%887a%26%23178%3B-4a%29-%285a%26%23178%3B-a-1%29%2B%282-a%26%23178%3B%2B4a%29%E7%9A%84%E5%80%BC)
当a=3时求多项式(7a²-4a)-(5a²-a-1)+(2-a²+4a)的值
当a=3时求多项式(7a²-4a)-(5a²-a-1)+(2-a²+4a)的值
当a=3时求多项式(7a²-4a)-(5a²-a-1)+(2-a²+4a)的值
原式=(7a²-5a²-a²)+(-4a+a+4a)+(1+2)
=a²+a+3
=9+3+3
=15
7*3*3-4*3-(5*3*3-3-1)+(2-3*3+4*3)=51-41+5=15
这个意思?????
(7a²-4a)-(5a²-a-1)+(2-a²+4a)=7a²-4a-5a²+a+1+2-a²+4a=a²+a+3=9+3+3=15