an+1=1−(an−1)2,an=12a_{n+1}=\sqrt{1-(a_n-1)^2} ,a_n=\frac{1}{2}an+1=1−(an−1)2,an=21，求：limn→∞∑i=1n(1−an)\lim_{n \to \infty} \sum_{i=1}^{n}(1-a_n)limn→∞∑i=1n(1−an)
