#COCR T1 Easy 数学式题解

废话多，请原谅

$\because \angle A+\angle B+ \angle C=180\degree$
$又\because \angle B=90\degree$
$\therefore \angle A+\angle C=180\degree-90\degree=90\degree$
$\because \angle A=2\angle C$
$\therefore \angle C=90\degree*\dfrac{1}{1+2}=30\degree,\angle A=90\degree-30\degree=60\degree$
$\because \sin(C)=\sin(30\degree)=\dfrac{1}{2}=\dfrac{AB}{AC}$
$\therefore AC=2AB$

Code:

#include <bits/stdc++.h>
using namespace std;
int main(){
	long double n;//其实没必要
    cin>>n;
    printf("%.2llf",2*n);
	return 0;
}