4(a+b)²-7(a+b)²+(a+b)²
=（4-7+1）（a+b）²
=-2(a+b)²
=-2(-1/2-3)²
=-2x49/4
=-49/2
=-24.5化简4(a+b)²-7(a+b)²+(a+b)²=（4-7+1）（a+b）²=-2(a+b)²Are you 确定？确定