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问题: 参数方程题

已知点p(x,y)为半圆C:x^2+y^2=1(x≥0)上的点,求x+y的最大值与最小值

解答:

半圆C:x^2+y^2=1(x≥0)的参数方程:
x=cosa, y=sina,(-Pi/2<=a<=Pi/2)
==> x+y =sina+cosa =(根号2)sin(a +Pi/4)
-Pi/4 <= a +Pi/4 <= 3Pi/4
==> -(根号2)/2 <= sin(a +Pi/4) <= 1
-1 <= x+y <= 根号2
x+y的最大值 =根号2, 最小值 =-1