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Mathematical forging
Solve the equation:

1, denominator removed

2. Remove the brackets

Step 3 move the project

4. Merger of similar projects

5, coefficient 1

I got fat:

Firstly, the invariants in the process of change are grasped and the equations are listed.

1, the problem of forging an object or replacing a container with a liquid, the volume (or volume) remains unchanged.

2, the length of the fixed object, although the shape and area of the surrounding graphics are different, but the total perimeter of the object should remain unchanged.

3, graphics splicing, cutting, translation, rotation and other types of problems, to grasp the graphics area and volume unchanged.

4. When mixing liquids with different concentrations, the total dissolved mass before and after mixing should remain unchanged.

Second, the perimeter is unchanged, the circular area is the largest and the rectangular area is the smallest.

Discount sales:

Profit = selling price-buying price

Profit rate = profit/cost × 100%

Purchase price = selling price-profit

Selling price = purchase price (1+ profit rate) = purchase price+profit.

Selling price = list price × discount quantity

Selling price-purchase price = purchase price × profit rate (profit)

List price × discount number-purchase price = purchase price × profit rate

Education savings:

Interest = principal × interest rate × number of periods

After-tax interest = interest ×( 1-20%)= principal × interest rate× number of installments ×( 1-20%)

Interest tax = interest ×20%

Sum of principal and interest = principal+after-tax interest = principal ×[ 1+ interest rate× number of periods ×( 1+20%)]

= principal+interest = principal ×( 1+ interest rate× number of periods)

Travel problems:

Meeting problem: speed and × meeting time = distance between two places.

Catch-up problem: speed difference × catch-up time = distance difference

Water flow problem: downstream speed = still water speed+water flow speed

Countercurrent velocity = still water velocity-current velocity

Downstream speed-countercurrent speed = 2 times of water flow speed.

Downstream speed+countercurrent speed = 2 times of still water speed.