4．The 20­kilometre­long subway is so far Guangzhou’s largest c________ project.

3．Many great people，such as Sun Yet­sen and Mao Zedong，were once active in the south，leaving behind many historical s________.

2．They will do their best to g________ more energy from the wind and sun.

1．Burning coal has led to g________ warming.

7．判斷y=－Asin(ωx+)(ω＞0)的單調(diào)區(qū)間，只需求y=Asin(ωx+)的相反區(qū)間即可，一般常用數(shù)形結(jié)合而求y=Asin(－ωx+)(－ω＜0＝單調(diào)區(qū)間時(shí)，則需要先將x的系數(shù)變?yōu)檎�的，再設(shè)法求之

6．函數(shù)的單調(diào)性是在定義域或定義域的某個(gè)子區(qū)間上考慮的，要比較兩三角函數(shù)值的大小一般先將它們化歸為同一單調(diào)區(qū)間的同名函數(shù)再由該函數(shù)的單調(diào)性來比較大小。

5．求三角函數(shù)式的最小正周期時(shí)，要盡可能地化為只含一個(gè)三角函數(shù)，且三角函數(shù)的次數(shù)為1的形式，否則很容易出現(xiàn)錯(cuò)誤。

4．求定義域時(shí)，若需先把式子化簡，一定要注意變形時(shí)x的取值范圍不能發(fā)生變化。

3．對于具有周期性的函數(shù)，應(yīng)先求出周期，作圖象時(shí)只要作出一個(gè)周期的圖象，就可根據(jù)周期性作出整個(gè)函數(shù)的圖象。

2．作函數(shù)的圖象時(shí)，首先要確定函數(shù)的定義域