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// 用二分查找，精度0.0001
function 二分开根号(x) {
  var start = 0, end = x,count=1;
  while (true) {
    var mid = start + (end - start) / 2;
    var sq = mid * mid;
    if (Math.abs(sq - x) < 1e-4) {
      console.info(mid,count);
      break;
    }
    if (sq < x) {
      start = mid;
    } else if (sq > x) {
      end = mid;
    } else {
      console.info(mid,count);
      break;
    }
    count++;
  }
}
二分开根号(10);
// 3.1622695922851562  18次循环

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// 用牛顿迭代，精度0.0001
function 牛顿开根号(a) {
  // n_ = (n+a/n)/2;
  var n = 1, count = 1;
  var n_ = (n + a / n) / 2;
  while (Math.abs(n - n_) > 1e-4) {
    n = n_;
    n_ = (n + a / n) / 2;
    count++;
  }
  console.log(n_, count)
}
牛顿开根号(10);
// 3.162277660168379   6次循环