Mathematics cross law problem questions, how to use the mathematics cross method

Go to the chemistry competition book by yourself, and there should be chemical calculations in it.

We often say that the cross method is actually the cross comparison method, which is a graphical method. The cross diagram method is actually a simple algorithm instead of the summation formula, which is particularly suitable for the calculation of mixtures of two total quantities and two relationships (i.e., the calculation of 2-2 type mixtures), which is used to calculate the ratio of the two components in the mixture.

The cross elimination method is referred to as the cross elimination method, which is a type of ion inference problem solution, using "cross elimination" to narrow the scope of unknown substances, so as to use the problem to determine the substance and find the correct answer.

The criss-cross method is often used to calculate:

1) Calculation of mass fraction;

2) calculations on the average relative molecular weight;

3) the calculation of the average relative atomic mass;

4) the calculation of the average molecular formula;

5) Calculation of the heat of reaction;

6) Calculations regarding the reaction of the mixture.

It's just a solution to a binary equation.

x + y = 1

ax + by = c

c is between a and b, solve: x; y

There are 4 cases:

1) 7 9 rings, 3 10 rings.

2) 5 x 9 rings, 1 x 8 rings, 4 x 10 rings.

3) 3 x 9 rings, 2 x 8 rings, 5 x 10 rings.

4) 1 x 9 rings, 3 x 8 rings, 6 x 10 rings.

In the fourth type, 10 rings have more arrows than 9 rings

Select (d).

Give me an email address, I'll give you a document, and you'll understand it when you read it.

Solve the factorization of quadratic trinomial ax + bx+c.

For example: 2x -5x-12=(2x+3)(x-4) Through observation, it is found that 2x x=2x is the first term, 3 (-4)=-12 is the last term, and 2x (-4)+3 x=-5x is the middle term.

That is, the 2 of the first term is decomposed into 2 and 1, and the last term -12 is decomposed into 3 (-4) and the cross multiplication and then addition are the middle terms.

For example, an equation is 3x 2-x-2=0, and its two coefficients are 3 and -2 respectively, 3 can be split into 1*3, and -2 can be split into 2*(-1), which can be written.

3 2 is 1*2+3*(-1)=1 (the coefficient of the first square is -1), then the equation can be written as (x-1)*(3x+2)=0, and the two roots are x=1 and x=-2 3

For example, 5x 2-8x-4=0, you can split 5 into 1*5, and -4 can be split into 2*(-2), that is, 1 -2

5 2 i.e. 1*2+5*(-2)=(-8) ; x-2)*(5x+2)=0

If you can't split it, then honestly use the root finding formula.

It's quick to do more questions, and it can be a bit slow at first.

It can be understood that ax +bx+c=0 m n=c m+n=b m n must be an integer, and if you can't take an integer, then you have to use another way.

For example, x +5x+6=0 can be solved like this: 6=2 3 5=2+3 (x+2)(x+3)=0 x1=-2 x2=-3

There are formulas, and there are other simple methods, but the specific problem method is different. Equation x=(-b+- root number b-squared-4ac) -2a

Definitely yes, there are usually two.

It's hard to work with.

I didn't understand it, but I was quick to solve the problem with this.

Hehe, that "5 years later" is a completely useless redundant word. The landlord can remove "5 years later" from the problem and solve the problem, and you will understand.

To elaborate, that ratio has nothing to do with five years from now, but just how the sum will change if the numbers increase in the current parts.

Because five years later, it will increase on the basis of the current population.