javascript - 二次方程。获取ABC

Question

大家好。我想制作一个可以求解二次方程的程序，例如：0 = ax^2+bx+c。我可以使用变量 a、b、c 来解决它。问题是您必须手动选择 a、b 和 c。有没有办法从这样的方程中获取变量？0 = 5x^2 + 4x + 3 这里我们会得到 a = 5 b = 4 c = 3

顺便说一句，我正在用javascript做。我希望你能帮帮我

Answer 1

This should be more than enough to get you going; some assembly required.

Do you know if the Y value will always be on the left? Whether you'll ever see the form Ax^2 + Bx + C = 0 may add a step or two; I'll assume Y will always be on the left.

1. I would start by removing all white-space from the string.
   • quadratic = quadratic.replace(/ /g,'');
2. Then split the string by = and work with the right side.

3. Extract your variables (while preserving negatives).

   • var A = quad.match(/([-]?\d+)(?=[a-zA-Z]\^2)/);
     quadratic = quadratic.match(/-?\d+[a-zA-Z]\^2/,'');
     
     var B = quadratic.match(/-?\d+(?![a-zA-Z]\^)(?=[a-zA-Z])/);
     quadratic = quadratic.replace(/-?\d+[a-zA-Z]/,'');
     
     var C = quadratic.match(/-?\d+/);
     

4. Plug that into (-B ±√(B² - 4AC))/2a and test the results

   • You obviously have to do two separate functions as there is no ± operator.
   • Hint: squared is Math.pow(x,2) and square root is Math.pow(x,.5) or Math.sqrt(x).
   • Remember that if the discriminate is >0 there are two real solutions, =0 there is one real solution, or <0 there are no real solutions (but two complex solutions).

Answer 2

我认为拆分方法在这里可以为您工作：http: //www.w3schools.com/jsref/jsref_split.asp 首先将字符串拆分为“+”，然后将每个字符串拆分为“x”，然后获取第一个元素三个数组。

这假定添加的每个函数都具有相同的格式。您必须将所有减号变成加号（通过使乘数为负），或者检查以拆分减号。