2. Divide the figure into two completely symmetrical parts with a dotted line, which is called the symmetry axis.

3. The reflection is symmetrical up and down. When looking in the mirror, the front and back, up and down positions remain the same, only the left and right positions are reversed, which belongs to mirror symmetry. You can find a figure that is symmetrical to its mirror.

There are two ways to look at the time on the clock in the mirror:

① Take the straight line where the straight line 6, 12 is located as the symmetry axis, fold it in half from left to right, and draw a symmetrical pointer, which is real-time.

② Look at the back of the test paper.

4. Rectangular, square and circle are symmetrical figures.

A rectangle has two axes of symmetry. A square has four axes of symmetry. A circle has countless axes of symmetry.

5. Requirements for drawing symmetry axis: 1, ruler 2, dotted line 3, cross diagram 4, drawing standard.

6, according to the given figure, draw the other half of the symmetry method:

First find the axis of symmetry, draw a symmetrical point according to the axis of symmetry, and then connect the lines.

7. Be able to find out from which direction the character looks at the object.

Commonly used quantitative relations

1, number of copies × number of copies = total; Total number of copies/number of copies = number of copies; Total copies/number of copies = number of copies

2, 1 multiple× multiple = multiple; Several multiples ÷ 1 multiple = multiple; Multiply/Multiply = 1 Multiply

3. Speed × time = distance; Distance/speed = time; Distance/time = speed

4. Unit price × quantity = total price; Total price/unit price = quantity; Total price ÷ quantity = unit price

5. Work efficiency × working hours = total workload; Total amount of work ÷ work efficiency = working hours

Mathematical algorithm

1, additive commutative law: a+b = b+a.

The two addends exchange positions, and the sum remains the same. This is called additive commutative law.

2. Additive associative law; (a+b)+c=a+(b+c)

Add the first two numbers or add the last two numbers first, and the total remains the same. This is the so-called law of additive association.

3. Multiplicative commutative law: a× b = b× a.

Exchanging the positions of two factors and keeping the product unchanged is called multiplicative commutative law.

4. Multiplicative associative law: (a×b)×c=a×(b×c) or a×b×c=a×(b×c).

Multiply the first two numbers or multiply the last two numbers first, and the product remains the same. This is the so-called multiplicative associative law.

5. Multiplication distribution law: (a+b)×c=a×c+b×c or (a-b) × c = a× c-b× c.

Inverse application of the law of multiplication and distribution: a×c+a×b=(a+b)×c or a× c-b× c = (a-b )× c.