最新七年级上角平分线练习题及答案教学文案

角平分线相关练习题
答案：
1、∠DOC=30°
解析：由角平分线定义：到角两边距离相等的点在角平分线上，得知，点C在角平分线上，即OC为∠AOB
的角平分线，因为∠AOB=60°，所以∠DOC=∠EOC=30°
2、∠BOC=50°
解析：由题知，∠AOE=∠BOE=½∠AOB=45°，∠BOD=∠EOD－∠BOE=70°-45°=25°，∠BOC=2∠BOD=50°
3、D
解析：由角平分线定义和性质得知，角平分线上的点到角两边的距离相等，故A、B、C均正确。

4、S△BDC=½mn
解析：通过D点向BC边作垂线段，交BC于点E，则DE为△BDC的高线，由于DA⊥AB且DE⊥BC，BD是
角平分线，故得知线段AD=DE=m，S△BDC=½BC×DE=½mn
5、A
解析：由角平分线性质得知，角平分线上的点到角两边的距离相等，故P到AB的距离＝PE=3
6、∠COE=75°
解析：∠AOC=∠BOC=∠BOD=½×90°=45°，因为∠BOD=3∠DOE，所以∠BOE=⅔∠BOD=⅔×45°=30°，
∠COE=∠BOC+∠BOE=45°+30°=75°
7、∠BOD=75°
解析：∠COD=∠AOD=½∠AOC=½（∠AOB-∠BOC）=½（90°－60°）=15°，
∠BOD=∠BOC+∠COD=60°+15°=75°
8、∠AOC=140°
解析：∠AOC=∠AOB+∠BOC=2∠BOD+2∠BOE=2∠BOD+2（∠DOE-∠BOD）=2∠DOE=2×70°=140°
it 6 Science and Technolo t I Warming
escript.
Thai silk is known for its beauty and elegance. But a research team has found a new use for it. A bulletproof vest made of si s put to the test at a shooting range in Thailand. After several rounds of gunfire, the vest was examined. The bullets were stu he first layer of fifteen pieces of silk. A member of the research team says while silk threads may be soft, they can be used duce a stronger yarn than copper threads, the material used in regular bulletproof ves American and Japanese researchers say they are a step closer to predicting severe weather in and around the Indian Ocea earchers have analyzed weather data from the region over the past 40 years and they've discovered a strong connecti ween extreme weather and conditions in the ocean. A BBC science correspondent says the findings could make it easier dict droughts or, indeed, periods of heavy rainfa The world chess champion Garry Kasparov began a match against the rest of the world on the Internet. Kasparov made his fi ve with a meter-high pawn before an audience of chess fans at a park in New York. The move was immediately posted on cial website set up by the Microsoft corporation. Visitors to the site have 24 hours to vote on their counter move helped by
m of young chess experts who will suggest strategie Few scientific advances of this or any millennium can rival in significance the discovery of the structure of DNA, the bas lecule of life. Knowledge of the structure of DNA helps explains many things, including genetic mutation and , through lution. Understanding its code has helped to unlock the mechanics of inherited disease, as well as beneficial biological tra h as intelligence and body strength. The discovery of the DNA molecule also paved the way for many of today’s cutting-ed ences, including genetic engineering, a controversial branch of knowledge that raises new ethical and moral questions that a ain to be with us far into the next millennium.
Some say it's hard to find good help these days, but a Japanese electronics firm thinks it's found the answer. It's a robot th s and understands orders. The robot from NEC can record and send video mail through the Internet and switch on TVs a Rs. And if it's becoming a bit warm for you, one simple command and the robot will switch on the air conditioner. escript:
. Yes, you see, it's the force of attraction between any two objects. The strength of the force depends on the mass of the objec the distance between them. Er... the most obvious effect is the way objects on the surface of the earth are attracted towards t ter of the earth . as it comes down it goes relatively slowly 100 to 1,000 miles per hour and you can't see it, but the return stroke goes up fro earth to the cloud and it goes at over 87,000 miles per hour and that's the one you can see, you see, the one that goes back u really just a very large, powerful spark. The distance in miles you are away from it is the time in seconds between it and t nd you hea .. Well, they were first discovered in 1895 and they can penetrate matter that is opaque to light. Some matter is mo nsparent to them than others, which means you can see inside somebody. They are actually quite dangerous and people w rk with them wear special protective clothing . ordinary light consists of electromagnetic waves of different frequencies and phase(s). This is a。