第1.2.3牧场的面积依次为3.5.7公顷,三个牧场的草长得一样密,而且长得一样快,有两群牛,第一群牛

设X为数据总数,Y为第三组数据个数,则有X+Y=160+360,Y=0.4X,解方程得Y=120.

一车间：40÷（12-8）×8=80人
二车间：80÷8×12=120人
三车间：80÷8×21=210人

1 one first 1st
2 two second 2nd
3 three third 3rd
21 twenty-one twenty-first 21st
22 twenty-two twenty-second 22nd
23 twenty-three twenty-third 23rd
注：在英语中是没有22th这种说法的.

90-54=36千克36÷4=9千克/箱

提示β=（α+β）-α 然后2角差的正弦公式 答案16/65
提示α+β+π=（5π/4+β）-（π/4-α） -sin（α+β+π）=sin（α+β）后2角差的正弦公式注意π/4-α是第四象限角正弦值为负5π/4+β是第三象限角余弦值也为负 答案56/65
分步求解先算出tanβ再两角和的正切公式算出tan（α+β）再来一次两角和的正切公式算出tan「（α+β）+β」 答案1
2角和正切公式的变形运用tanα+tanβ=「tan（α+β）」（1-tanαtanβ）=tan（α+β）-tanαtanβtan（α+β）把在2角和正切公式的基础上2边同时乘以（1-tanαtanβ）
怎么晚了还给你打怎么多字不选我你好意思吗?

C D D

动能守恒没有找到～
牛顿第一定律：
The first law describes a fundamental property of matter,called inertia,as follows:
Every body remains in a state of rest or in a state of uniform motion (constant speed in a straight line) unless it is compelled by impressed forces to change that state.
牛顿第二定律
Newton's second law describes the manner in which a force compels a change of motion,at a rate of change called acceleration.It can be stated as follows:
Change of motion is proportional to the impressed force and takes place in the direction of the straight line in which that force is impressed.
牛顿第三定律：
Newton's third law may be stated as follows:
Action and reaction are equal and opposite.
This law is often expressed as “for every action there is an equal and opposite reaction.”
热力学第一定律
First law of thermodynamics,about the conservation of energy
The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to the system and the work done on the system.
热力学第二定律
Second law of thermodynamics,about entropy
The total entropy of any isolated thermodynamic system tends to increase over time,approaching a maximum value.
热力学第三定律
Third law of thermodynamics,about absolute zero temperature
As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as:"the entropy of all systems and of all states of a system is zero at absolute zero" or equivalently "it is impossible to reach the absolute zero of temperature by any finite number of processes".
动量守恒原理
Conservation of momentum
The principle of conservation of momentum states that the total momentum of a closed system of objects (which has no interactions with external agents) is constant.One of the consequences of this is that the centre of mass of any system of objects will always continue with the same velocity unless acted on by a force outside the system.
其他基本概念：
万有引力定律:
Newton's Law of Gravity
Each object in the universe attracts each other body.
能量守恒：
Conservation of energy states that the total amount of energy in an isolated system remains constant,although it may change forms (for instance,friction turns kinetic energy into thermal energy).
Put simply,the law of conservation of energy states that energy can not be created or destroyed—it can only be changed from one form to another (such as electrical energy into heat energy).