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18. 如图,在平面直角坐标系中,边长为2的正方形$OA_{1}B_{1}C_{1}$的两边在坐标轴上,以它的对角线$OB_{1}$为边作正方形$OB_{1}B_{2}C_{2}$,再以正方形$OB_{1}B_{2}C_{2}$的对角线$OB_{2}$为边作正方形$OB_{2}B_{3}C_{3}$……以此类推,则正方形$OB_{2020}B_{2021}C_{2021}$的顶点$B_{2021}$的坐标是
$(-2^{1011}, - 2^{1011})$
.答案
$(-2^{1011}, - 2^{1011})$
19. (6分)计算:
(1)$\sqrt [3]{-27}+|3-\sqrt {5}|-(\sqrt {9}-\sqrt [3]{8})^{2}+3\sqrt {5}$;
(2)$\sqrt {16}-\sqrt [3]{-8}-\sqrt [3]{1}+\sqrt {1+\frac {9}{16}}$.
(1)$\sqrt [3]{-27}+|3-\sqrt {5}|-(\sqrt {9}-\sqrt [3]{8})^{2}+3\sqrt {5}$;
(2)$\sqrt {16}-\sqrt [3]{-8}-\sqrt [3]{1}+\sqrt {1+\frac {9}{16}}$.
答案
(1)$-1 + 2\sqrt{5}$；(2)$\frac{25}{4}$
