Question

嗨我正在大学学习java，我刚刚完成了一段计算BMI的代码，就像这样，num1是千克，num2是厘米（（num1 / num2）/ num2）* 10000 ; 当我向老师展示这个等式时，他告诉我这是不正确的，正确的是 num1 /（（num2 * num2）/ 10000）; 当我测试两行代码时得到了相同的结果，但他告诉我，我需要证明两条线都像AxB和BxA一样，但是我没有找到方法来证明它们是相同的，但我确实知道它们是如何' d是一样的。我的问题是，它们都是一样的吗？

如果我将70 KG作为体重，将175 CM作为身高，那么它会说出22.9的线条（记住这是我的等式）。和我的老师一样，它会是一样的。但他不相信他们是一样的。这是我的代码：

import javax.swing。*; import java.util.Scanner;

class apples {

public static void main (String args[]) {
    String fsum; /* this is a variable declaration*/
    String sum; /* this is a variable declaration*/
    double answer; /* this is a variable declaration*/
    double num1, num2; /* this is a variable declaration*/
    String anything; /* this is a variable declaration*/
            Scanner Tahmid = new Scanner (System.in);/*Scanner Variable*/
    System.out.println("This program was created by Tahmid Ahmed on 01/10/2013\nThis program would allow you the user to be able to calculate your BMI");
    System.out.println("To continue please click enter");/*Output*/
    anything = Tahmid.nextLine();/*Input as a break*/
    fsum=JOptionPane.showInputDialog("Please enter weight in Kilograms (KG) "  ); /*Popup box to allow weight to be entered*/
    sum=JOptionPane.showInputDialog("Please enter height in Centimetres (CM) ");/*Popup box to allow height to be entered*/
    num1 = Double.parseDouble(fsum);/*Conversion of String into Double*/
    num2 = Double.parseDouble(sum);/*Conversion of String into Double*/

    answer = num1/((num2*num2)/10000);/*<<<<<<<<-----My teachers Equation*/ /*My Equation ---- >>>>>> ((num1/num2)/num2)*10000       */
    if (answer<=18){
    JOptionPane.showMessageDialog(null, "Your total BMI levels are: " + answer, "You're underweight! Eat some more!", JOptionPane.INFORMATION_MESSAGE);
        }
    else if(answer>=25){
    JOptionPane.showMessageDialog(null, "Your total BMI levels are: " + answer, "You're overweight now bro! Eat Less!", JOptionPane.INFORMATION_MESSAGE);   }

    else if(answer<25) {
    JOptionPane.showMessageDialog(null, "Your total BMI levels are: " +answer, "You're the perfect weight! Stay that way :)", JOptionPane.INFORMATION_MESSAGE);}


}

}

Answer 1

它们在数学上是等价的，但在浮点数上不等效。你的老师试图指出所有的乘法应该在所有的分割之前进行，这样才能达到最大的精度。 num2*num2周围的括号确保首先计算它。

Answer 2

只要玩代数，很明显它们是等价的：

((num1/num2)/num2)*10000  ??  num1/((num2*num2)/10000)
((num1/num2) * (1/(num2)) * 10000   ??   num1 / (num2^2 / 10000)
(num1 / num2^2) * 10000  ??  num1 * (10000 / num2^2)
10000 * num1 / num2^2  ==  10000 * num1 / num2^2

这些方程式是否相同？

2 个答案: