Question

若a-b=4 则1/2(a^2+b^2)-ab

2n^2-28n+98 因式分解

Answer 1

（1），原式=1/2(a^2+b^2)-1/2*2ab
=1/2(a^2+b^2-2ab)用完全平方公式
=1/2(a-b)^2
=1/2*16=8
(2),原式=2(n^2-14n+49)
=2(n-7)^2

Answer 2

1/2(a^2+b^2)-ab=1/2(a^2-2ab+b^2)=1/2(a-b)^2=(1/2)*4^2=8
2n^2-28n+98=2*(n^2-14n+49)=2*(n-7)^2