问题
填空题
等比数列1,2,4…的前10项的和为______.
答案
根据题意,可得等比数列的首项为1,公比为
=2,2 1
则S10=
=210-1=1023;1(1-210) 1-2
故答案为1023.
等比数列1,2,4…的前10项的和为______.
根据题意,可得等比数列的首项为1,公比为
=2,2 1
则S10=
=210-1=1023;1(1-210) 1-2
故答案为1023.
Look at the pictures and choose the correct answers. 看图,选择正确答案。 |
( )1. — ? —She is hanging up the phone. A. What is Jenny doing? B. What does Jenny do? C. What did Jenny do? | ![]() |
( )2. —Where is she? — . A. She's washing vegetables. B. She's in the store. C. She's in the kitchen. | ![]() |
( )3. —What's Danny doing? — . A. He's talking on the phone. B. He's making a call. C. He makes a call. | ![]() |