Grade five math: It is known that the area of the shadow part (isosceles triangle) in the lower trapezoid is 15 square centimeter, and the bottom of the trapezoid is 20 centimeters. Find the trapezoid

Grade five math: It is known that the area of the shadow part (isosceles triangle) in the lower trapezoid is 15 square centimeter, and the bottom of the trapezoid is 20 centimeters. Find the trapezoid. If you want to know how to shoot backlight, you should shoot it. To understand what backlight is. In the process of shooting creation, it is often light. In the theme shooting of this lamp, we often talk about the problems between backlights.

As shown in the figure, when the light source shoots at the position of "3. 1" relative to the subject at point A, the light is called backlight. When the light source moves from point A and point C to point B, this is the so-called side B of the backlight. When the light source is at the lower E point, this is the position of the so-called planar backlight. When the light moves from point E to point D, the light source increases, which is the so-called inclined backlight. We often say that the backlight source, except for indoor shooting with special lighting, is usually in the backlight sunlight, and the position of this light source is ever-changing with the passage of time, which brings difficulties to beginners to shoot in the backlight. However, once you have the basic skills of backlight photography, the difficulties will be solved.

Master the characteristics of backlight. Because of the low-angle light in the morning and evening, the light goes out of the flat track. From the illumination of the subject, the sun is low on the back of the subject, and the projection of the subject is very long, high and low. This thing is on the side of backlight or backlight, which helps to highlight the main body and outline the figures and scenery. Beautiful figures reflect the ideal shape and create rich light depth. At that moment in the scene, under other lighting conditions, clutter becomes simple and expressive. When shooting the central tower, the author chose a low-angle sunset, and the afterglow of the sun outlined the outline of the central tower, so that the CCTV building at this time was surrounded by messy buildings, hiding a touch of low-color sunset, and the film showed warm colors, thus highlighting the theme and taking a simple silhouette photo (Figure 2).

Third, pay attention to correct exposure. The key to choosing the correct exposure is to take good photos, which are suitable for beginners. Backlight photo shooting and. If you take a general commemorative photo just to take a good photo of a person, you need to clearly state that the person has to face the photometric data to shoot. In the case of large light ratio, if you measure a person's face, it is easy to make people exposed normally; Background overexposure phenomenon, at this time, the flash should be used appropriately to make the theme and character background completely exposed (Figure 3). If you put a close-up or other people's questions, the brightness of a person's face should still be the object of photometric shooting in the shadow area. If the photo is taken in silhouette, it should be taken with the brightness of the measured background.

Note: When shooting backlight, the proper use of light string will blur the subject. If you take a black-and-white photo, the developed photo will be white and bright, which will affect the beauty of the photo, and the photo with heavy makeup will become a piece of scrap iron. If you shoot with color film, the light will change the picture of the chord. If not handled properly, strings will increase the artistic conception of light as the theme.

For beginners of backlight photography, we suggest using trapezoidal exposure method, so that the possibility of taking photos will be stronger, the choice will be greater and the opportunities will be more.