The Basics of Math—Made Clear

    Basic Math introduces students to the basic concepts of mathematics, as well as the fundamentals of more tricky areas. These 30 fantastic lectures are designed to provide students with an understanding of arithmetic and to prepare them for Algebra(代数) and beyond.

    The lessons in Basic Math cover every basic aspect of arithmetic. They also look into exponents(指数), the order of operations, and square roots. In addition to learning how to perform various mathematical operations, students discover why these operations work, how a particular mathematical topic relates to other branches of mathematics, and how these operations can be used practically.

    Basic Math starts from the relatively easier concepts and gradually moves on to the more troublesome ones, so as to allow for steady and sure understanding of the material by students. The lectures offer students the chance to “make sense” of mathematical knowledge that may have seemed so frightening. They also help students prepare for college mathematics and overcome their anxiety about this amazing—and completely understandable—field of study.

    By the conclusion of the course, students will have improved their understanding of basic math. They will be able to clear away the mystery(神秘性) of mathematics and face their studies with more confidence than they ever imagined. In addition, they will strengthen their ability to accept new and exciting mathematical challenges.

    Professor H. Siegel, honored by Kentucky Educational Television as “the best math teacher in America,” is a devoted teacher and has a gift for explaining mathematical concepts in ways that make them seem clear and obvious. From the basic concrete ideas to the more abstract problems, he is master in making math lectures learner-friendlier and less scary.

    With a PhD in Mathematics Education from Georgia State University, Dr. Siegel teaches mathematics at Central Arizona College. His courses include various make-up classes and a number of lectures for future primary school teachers.

    If the course fails to provide complete satisfaction to you, you can easily exchange it for any other course that we offer. Or you can get your money back.

小明用焦距为10cm的凸透镜探究凸透镜成像的规律，他将烛焰放在距凸透镜15cm的位置，调节光屏位置，可以得到一个清晰的倒立、 ____（选填“等大”、“放大”或“缩小”）的实像，利用这个原理可以制成 ____．实验中他不慎用手指尖触摸到了凸透镜，此时光屏上 ____（选填“会”或“不会”）出现手指尖的像．

    Ever wonder how much a cloud weighs? What about a hurricane? A meteorologist（气象学家） has done some estimates and the results might surprise you.

    Let's start with a very simple white puffy cloud—a cumulus cloud(积云). How much does the water in a cumulus cloud weigh? Peggy LeMone, senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, did the numbers. “The water in the little cloud weighs about 550 tons,” she calculates. “Or if you want to convert it to something that might be a little more meaningful...think of elephants.” Assume（假设） an elephant weighs about six tons, she says, that would mean the water inside a typical cumulus cloud would weigh about one hundred elephants.

    The thought of a hundred elephants' worth of water floating in the sky begs another question—what keeps it up there?

    “First of all, the water isn't in elephant-sized particles(微粒); it's in tiny tiny tiny particles,” explains LeMone. And those particles float on the warmer air that's rising below. But still, the concept of so much water floating in the sky was surprising even to a meteorologist like LeMone. “I had no idea how much a cloud would weigh, actually, when I started the calculations（计算）,” she says.

    So how many elephant units of water are inside a big storm cloud—10 times bigger all the way around than the “puffy” cumulus cloud? Again, LeMone did the numbers: About 200,000 elephants.

    Now, come to the calculations for a hurricane about the size of Missouri and the figures get really massive. “What we're doing is weighing the water in one cubic meter theoretically pulled from a cloud and then multiplying by the number of meters in a whole hurricane,” she explains.

    The result? Forty million elephants. That means the water in one hurricane weighs more than all the elephants on the planet. Perhaps even more than all the elephants that have ever lived on the planet.

未成年人遇到不法侵害，应该（   ）
①以牙还牙，用非法手段进行报复    
②运用法律武器维护自己的合法权益
③忍气吞声，自认倒霉，以防遭到更大的侵害    
④敢于斗争，善于周旋，寻求法律保护，依法阻止不法侵害行为  

下面是以小麦为实验材料所进行的实验，其中叙述正确的是（   ）