某公司生产一种新产品，前期投资300万元，每生产1吨新产品还需其他投资0.3万元，如果生产这一产品的产量为x吨，每吨售价为0.5万元．
（1）设生产新产品的总投资y1万元，试写出y1与x之间的函数关系式和定义域；
（2）如果生产这一产品能盈利，且盈利为y2万元，求y2与x之间的函数关系式，并写出定义域；
（3）请问当这一产品的产量为1800吨时，该公司的盈利为几万元？
（1）由题意，得
y1=0.3x+300，定义域为x＞0．
（2）由题意，得
y2=0.5x-0.3x-300，
y2=0.2x-300；
定义域为x＞1500；
（3）当x=1800时，y2=0.2×1800-300=60．
故当这一产品的产量为1800吨时，该公司的盈利为60万元．
| 阅读对话，从下列所给的句子中，选出合适的句子补全对话。 | |
| Brad: So, Paula, where are you from? Paula: I'm from Canada, originally. Brad: From Canada? 1. Paula: I was born in Toronto. Brad: 2. Paula: We moved here when I was fourteen. Brad: Did you go to school here? Paula: Well, I went to high school here, but 3. Brad: Did you get a job right after graduation? Paula: No, I traveled for a while in Europe after college, and then 4. Brad: When was that? Paula: Let's see… That was about six years ago. Brad: I bet that was interesting. 5. Paula: I studied French. Anyway…that's enough about me. How about you? Were you born in L.A.?
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