When you zoom in on a photo, it becomes larger, but the face is not stretched or flattened. The photo was expanded: everything grew at the same rate. Enlarge without deforming Propriedade · The magnification rule To enlarge or reduce a figure without deforming: multiply all sides by same number; keep the angles (the corners) the same. If the number is greater than 1, the figure is enlarged; if it is less than 1, such as ½, it is reduced.
To fence a vegetable garden, you need to know how much wire goes around it. To plant, you need to know how much floor is inside. There are two different measurements: the perimeter and the area. Perimeter: the path around Definição · Perimeter The perimeter is the measurement of the contour of a figure: it is the sum of the lengths of all sides. An ant that goes around a rectangular table measuring 2 m by 1 m walks 2 + 1 + 2 + 1 = 6 m. This is the perimeter of the table.
Fold a sheet in half, cut out a design on the fold and open it: the two halves are equal, one “reflecting” the other. This figure has symmetry. The axis of symmetry Definição · Axis of symmetry A figure has axis of symmetry when there is a line that divides it into two halves that meet fit perfectly when folding the figure along this line. Each half is the reflection of the other in a mirror.
Draw a figure using only straight line pieces, without taking the pencil off the paper, until you return to the beginning without crossing the path. You drew a polygon! What is a polygon Definição · Polygon A polygon is a flat closed figure, formed only by pieces of straight lines (the sides) that do not intersect. The points where two sides meet are the vertices. The circle is not a polygon: its contour is curved. An open figure is also not a polygon.
When you open a door, turn a doorknob, or turn right around a corner, you are making a turn. The size of this rotation is what we call angle. How much did you spin? One full turn: you turn until you look at the same place again. Half turn: you turn your back to where you were looking. Quarter turn: you turn to the side, like a corner. This rotation forms a right angle. Mathematicians divide the entire revolution into 360 equal parts, called degrees (°). So half turn has 180°, and a quarter turn has 90°.
A stretched thread, the path of an ant, the outline of a cloud: these are all lines. Some are straight, others curve. Straight and curved, open and closed A straight line does not change direction, like a tightly stretched string. A curved line changes direction all the time, like the path of a snake. A closed line ends where it began, like the outline of a circle. An open line has two loose ends. A line made only of straight pieces is a polygonal. When it is closed, it draws a polygon.
Look around you. The lid of a jar, the bedroom door, a slice of pizza, the road sign: each one resembles a geometric shape. Flat shapes and non-planar shapes A shape is flat when it fits entirely on a sheet of paper, without “bulk”. A drawing in the notebook, the shadow of an object and the outline of a coin are flat shapes. A shoe box, a ball and a can are not flat: they have volume and take up space. But notice: the faces of the box are rectangles, and the lid of the can is a circle. Flat shapes are “glued” to the surface of objects.