题干

已知2a﹣1的平方根是±3,3a+b﹣1的立方根是4,求a+b的平方根.
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解:∵2a﹣1的平方根是±3,∴2a﹣1=9,∴a=5,∵3a+b﹣1的立方根是4,∴3a+b﹣1=64,∴b=50,∴a+b=55,∴a+b的平方根是 ±55

同类题1

阅读《自动调温电熨斗》,回答:

自动调温电熨斗

    图甲、乙分别是电熨斗的实物图和结构示意图.常温时,双金属片端点上的触点A与弹性铜片上的触点B相接触.当电熨头与电源接通时,电流通过相接触的铜片、双金属片,流过发热板(电热丝),发热板发热并将热量传给电熨斗底部的金属底板,人们就可用发热的底板熨烫衣物了.双金属片是把长和宽都相同的铜片和铁片紧紧地铆在一起做成的.受热时,由于铜片膨胀得比铁片大,双金属片便向铁片那边弯曲.温度愈高,弯曲得愈显著.随着通电时间增加,底板的温度升高到设定温度时,与底板固定在一起的双金属片受热后向下弯曲,双金属片顶端的触点A与弹性铜片上的触点B分离,于是电路断开.这时底板的温度不再升高,并随金属底板的散热而降低;双金属片的形变也逐渐恢复,当温度降至某一值时,双金属片与弹性铜片又重新接触,电路再次接通,底板的温度又开始升高.这样,当温度高于所需温度时电路断开,当温度低于所需温度时电路接通,便可保持温度在一定的范围内自动调温了.

    怎样使电熨斗有不同温度范围呢?如将调温钮上调时,上下触点随之上移,双金属片只需稍微下弯即可将触点A、B分离.这时双金属片可控制金属底板在较低温度下的工作.若将调温钮下调时,上下触点A、B随之下移,双金属片必需下弯程度较大时,才能将触点分离.这时双金属片可控制金属底板在较高温度下的工作.这样便可适应织物对不同熨烫温度的要求了.

阅读上述材料,请回答下列问题:

同类题4

    Since the 1970s, scientists have been searching for ways to connect the brain with computers. Braincomputer interface(BCI) technology could help people with disabilities send commands to machines.
    Recently, two scientists, Jose Millan and Michele Tavella from the Federal Polytehnic School in Lausanne, Switzerland, show a small robotic wheelchair directed by a person's thoughts.
    In the laboratory, Tavella operated the wheelchair just by thinking about moving his left or right hand. He could even talk as he watched the vehicle and guided it with his thoughts.
    “Our brain has billions of body cells(细胞). These send signals through the spinal cord(脊髓) to the body part to give us the ability to move. But spinal cord injuries(脊柱受伤) or other conditions can prevent these weak electrical signals from reaching the body part.” Tavella says. “Our system allows disabled people to communicate with outer world and also to control machines.”
    The scientists designed a special cap for the user. This head cover picks up the signals from the scalp(头皮) and sends them to a computer. The computer finds meanings of the signals and commands the wheelchair with an engine. The wheelchair also has two cameras that tell objects in its path. They help the computer react to commands from the brain.
    Prof. Millan , the team leader, says scientists keep improving the computer software that finds meanings of brain signals and turns them into simple commands.” The practical possibilities that BCI technology offers to disabled people can be grouped in two kinds: communication, and controlling objects. One example is this wheelchair.”
    He says his team has set two goals. One is testing with real patients, so as to prove that this is a technology they can get advantages from. And the other is sure that they can use the technology for long.