Question

点p（x,y）在直线x+y-4+0上,则x平方+y平方的最小值是?

Answer 1

p（x,y）在直线x+y-4=0上:

x+y=4

y=4-x

x^2+y^2=x^2+(4-x)^2=x^2+16-8x+x^2

=2x^2-8x+16

=2(x-2)^2+8

即当X=2时,有最小值是：8