幾何及數學的幾種算計介紹

主要內容

• 1.規則多邊形已知邊數計算內角
• 2.規則多邊形已知邊數計算外角
• 3.規則多邊形已知外角求邊數
• 4.已知數字計算羅馬數字
• 5.已知三個頂點計算三角形的面積
• 6.判斷一個數是不是素數

1.規則多邊形已知邊數計算內角

function side(n) {
    var edgeNum = ((n - 2) * 180) / n;
    var inner = 180 - document.form1.intx.value;
    var outer = n*document.form1.intx.value;
}

2.規則多邊形已知邊數計算外角

function extn(edgeNum) {
    var inner = 360 / e;
    var outer = 180 - e;
}

3.規則多邊形已知外角求邊數

function intn(i) {
    var inner= 180 - i;
    var outter = 360 / (180 - i);
}

4.已知數字計算羅馬數字

var ones_numerals = new Array();
ones_numerals[0] = "";
ones_numerals[1] = "I";
ones_numerals[2] = "II";
ones_numerals[3] = "III";
ones_numerals[4] = "IV";
ones_numerals[5] = "V";
ones_numerals[6] = "VI";
ones_numerals[7] = "VII";
ones_numerals[8] = "VIII";
ones_numerals[9] = "IX";
var tens_numerals = new Array();
tens_numerals[0] = "";
tens_numerals[1] = "X";
tens_numerals[2] = "XX";
tens_numerals[3] = "XXX";
tens_numerals[4] = "XL";
tens_numerals[5] = "L";
tens_numerals[6] = "LX";
tens_numerals[7] = "LXX";
tens_numerals[8] = "LXXX";
tens_numerals[9] = "XC";
var hundreds_numerals = new Array();
hundreds_numerals[0] = "";
hundreds_numerals[1] = "C";
hundreds_numerals[2] = "CC";
hundreds_numerals[3] = "CCC";
hundreds_numerals[4] = "CD";
hundreds_numerals[5] = "D";
hundreds_numerals[6] = "DC";
hundreds_numerals[7] = "DCC";
hundreds_numerals[8] = "DCCC";
hundreds_numerals[9] = "CM";
var thousands_numerals = new Array();
thousands_numerals[0] = "";
thousands_numerals[1] = "M";
thousands_numerals[2] = "MM";
thousands_numerals[3] = "MMM";
function checkNumber(number) {
    if ((parseInt(number) < 4000) && (parseInt(number) > 0)) {
        var numeral = createNumeral(number);
        if (numeral.indexOf('undefined') == -1) {
            window.document.form.numeral.value = numeral;
        }
    } else {
        alert('請輸入一個有效的數字。');
    }
}
function createNumeral(num) {
    var new_num = num
    var thousands = Math.floor(new_num / 1000);
    new_num -= thousands * 1000;
    var hundreds = Math.floor(new_num / 100);
    new_num -= hundreds * 100;
    var tens = Math.floor(new_num / 10);
    new_num -= tens * 10;
    var ones = Math.floor(new_num / 1);
    if ((thousands == NaN) || (hundreds == NaN) || (tens == NaN) || (ones == NaN)) {
        alert('you must enter a valid number');
    } else {
        var array = new Array(thousands, hundreds, tens, ones);
        return makeNumeral(array);
    }
}
function makeNumeral(place_values) {
    var numeral = "";
    numeral += thousands_numerals[place_values[0]];
    numeral += hundreds_numerals[place_values[1]];
    numeral += tens_numerals[place_values[2]];
    numeral += ones_numerals[place_values[3]];
    return numeral;
}

5.已知三個頂點計算三角形的面積

function triangle(form) {
    var x1 = eval(form.x1.value);
    var y1 = eval(form.y1.value);
    var x2 = eval(form.x2.value);
    var y2 = eval(form.y2.value);
    var x3 = eval(form.x3.value);
    var y3 = eval(form.y3.value);
    form.answer.value = ((x1 * y2 + x2 * y3 + x3 * y1) - (x2 * y1 + x3 * y2 + x1 * y3)) / 2;
}

6.判斷一個數是不是素數

function prime(form) {
    var num = parseInt(form.number.value);
    if (isNaN(num) || num < 0) {
        form.result.value = (form.number.value + " is not a valid number!  Try again!");
    }
    if (num == 1 || num == 2) {
        form.result.value = (num + " is prime!");
    }
    for (var i = 2; i < num; i++) {
        if (num % i == 0) {
            var prime = "yes";
            form.result.value = (num + " is not prime.  It is divisible by " + i + ".");
            break;
        }
        if (num % i != 0) var prime = "no";
    }
    if (prime == "no") form.result.value = (num + " is prime!");
}

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