第1个回答 2019-12-10
证明:(必要性)设点P(x
,y)是y
=
f
(x)图像上任一点,∵点P(
x
,y)关于点A
(a
,b)的对称点P‘(2a-x,2b-y)也在y
=
f
(x)图像上,∴
2b-y
=
f
(2a-x)即y
+
f
(2a-x)=2b故f
(x)
+
f
(2a-x)
=
2b,必要性得证.(充分性)设点P(x0,y0)是y
=
f
(x)图像上任一点,则y0
=
f
(x0)∵
f
(x)
+
f
(2a-x)
=2b∴f
(x0)
+
f
(2a-x0)
=2b,即2b-y0
=
f
(2a-x0)
.故点P‘(2a-x0,2b-y0)也在y
=
f
(x)
图像上,而点P与点P‘关于点A
(a
,b)对称,充分性得征.