| （1）异分母分式相加减，先______变为______分式，然后再加减． （2）分式
（3）计算：
（4）计算：
|
（1）异分母分式相加减，先通分变为同分母分式，然后再加减；
（2）分式
，2 xy
，3 x+y
的最简公分母是xy（x+y）（x-y）；4 x-y
（3）原式=
；yz-2xz+3yz x2y2z2
（4）原式=
•x x-1
=2x-1 x
．2x-1 x-1
故答案为：（1）通分；同分母；（2）xy（x+y）（x-y）；（3）
；（4）yz-2xz+3yz x2y2z2 2x-1 x-1
Now in some places of our country, many people are cutting down (砍伐) the trees in the forests. They need more to build houses and more farmland to grow crops and so on. The areas of forests are getting . Some scientists say that there no big forests in 20 or 30 years. It is really a(n) thing. the forests, we will have sandstorms (沙尘暴) often. The weather will get . The earth will become a big desert (沙漠). A lot of plants and animals will . Crops will not grow anywhere. Life will be for everyone. So we should do our best our living environment and keep our mountains , the water clean, and the sky blue.
|
的交点恰好处于点划线上，说明船舶处于（）状态。