(-7+a+b)(7+a+b)

(-7+a+b)(7+a+b)
=((a+b)-7)((a+b)+7)
=(a+b)²-7²
=a²+2ab+b²-49

你好:
(-7+a+b)(7+a+b)
=[(a+b)-7)][(a+b)+7)]
=(a+b)²-7²
=a²+2ab+b²-49
这种题一般都有简便方法,要注意观察.

(-7+a+b)(7+a+b)=((a+b)-7)((a+b)+7)=(a+b)^2-7^2=a^2+2ab+b^2-49

(-7+a+b)(7+a+b)
=(A+B)^2-7^2
=A^2+2AB+B^2-49