1 rectangle
(1) function
A quadrilateral with equal opposite sides and four right angles. There are two axes of symmetry.
(2) Calculation formula
The length of a rectangle is represented by a, the width by b, the circumference by c and the area by s.
c=2(a+b)
s=ab
2 square
(1) Function:
A quadrilateral with four equal sides and four right angles. There are four axes of symmetry.
(2) Calculation formula
The side length a of a square is represented by, the perimeter is represented by c, and the area is represented by S.
c=4a
s=a2
3 triangle
(1) function
A figure surrounded by three line segments. The sum of internal angles is 180 degrees. The triangle is very stable. A triangle has three heights.
(2) Calculation formula
s=ah÷2
(3) Classification
Divide by angle
Acute triangle: all three angles are acute.
Right triangle: One angle is a right angle. The two acute angles of an isosceles triangle are 45 degrees each, and it has an axis of symmetry.
Obtuse triangle: One angle is obtuse.
Divide by edge
Unequal triangle: The three sides are not equal in length.
Isosceles triangle: two sides are equal in length; The two bottom angles are equal; There is an axis of symmetry.
Equilateral triangle: all three sides are equal in length; All three internal angles are 60 degrees; There are three axes of symmetry.
(2) Calculation formula
The base of a triangle is represented by a, the height by h and the area by s.
s=ah÷2
4 parallelogram
(1) function
Two sets of quadrilaterals parallel to opposite sides.
The opposite sides are parallel and equal. Diagonal angles are equal, and the sum of degrees of two adjacent angles is 180 degrees. Parallelogram is easy to deform.
(2) Calculation formula
The base a of the parallelogram is denoted by, the height is denoted by h, and the area is denoted by s.
S = ah
5 trapezoid
(1) function
There is only one set of quadrilaterals with parallel sides.
The center line is equal to half of the sum of the upper and lower bottoms.
An isosceles trapezoid has an axis of symmetry.
(2) Formula
The upper base of the trapezoid is represented by a, the lower base is represented by h, the center line is represented by m, and the area is represented by s.
s=(a+b)h÷2
s=mh
6 yuan
Understanding of (1) circle
A curved figure on a plane.
The point of the center of the circle is called the center of the circle. Generally represented by the letter o.
Radius: The line segment connecting the center of the circle and any point on the circle is called radius. Generally expressed by R.
In the same circle, there are countless radii, and each radius has the same length.
The line segment passing through the center of the circle with both ends on the circle is called the diameter. Generally represented by D.
The same circle has countless diameters, all of which are equal.
In the same circle, the diameter is equal to the length of two radii, that is, d=2r.
The size of a circle depends on its radius. A circle has countless axes of symmetry.
(2) Drawing a circle
Separate the two feet of the compass and determine the distance (radius) between the two feet;
Fix a foot on a point (that is, the center of the circle) with a needle tip;
Turn one foot with the tip of a pencil once and draw a circle.
(3) the circumference of a circle
The length of the curve forming a circle is called the circumference of the circle.
The ratio of the circumference to the diameter of a circle is called pi. Represented by the letter ∏.
(4) the area of the circle
The size of the plane occupied by a circle is called the area of the circle.
(5) Calculation formula
The radius of a circle is represented by R, the diameter by D, the circumference by C and the area by S.
c=πd=2πr
s=πr2
d=2r
r=
Seven departments
Understanding of (1) Plate
A figure surrounded by an arc and two radii passing through both ends of the arc is called a fan.
The part between two points AB on the circle is called arc, which is pronounced as "arc AB".
The angle of the vertex at the center of the circle is called the central angle.
In the same circle, the size of the sector is related to the central angle of the sector.
The sector has an axis of symmetry.
(2) Calculation formula
The radius of the sector is represented by r, n is the degree of the central angle, and the area is represented by s.
s=πnr2÷360
8 rings
(1) function
It is formed by subtracting two concentric circles with different radii, and there are countless symmetry axes.
(2) Calculation formula
s=π(R2-r2)
9 axisymmetric figure
(1) function
If a graph is folded in half along a straight line, the graphs on both sides can completely overlap, and this graph is an axisymmetric graph. The straight line where the crease lies is called the symmetry axis.
A square has four axes of symmetry, and a rectangle has two axes of symmetry.
An isosceles triangle has two axes of symmetry and an equilateral triangle has three axes of symmetry.
An isosceles trapezoid has one axis of symmetry, and a circle has countless axes of symmetry.
The diamond has four axes of symmetry, and the fan has one axis of symmetry. 60 。