7楼: Originally posted by shizijun at 2012-09-04 18:15:00
取最小值和次最小值！
kb = polyfit(,,1);
k = kb(1); b = kb(2);
k*x +b = -3 求得x就是你要的！

3楼: Originally posted by baobiao007 at 2012-09-03 15:26:04
如果知道这3个曲线的明确函数关系式，可以用fzero命令解出根。
比如：求y=x^2  与 y=30的交点

a=-10:10;
y=a.^2;
plot(a,y);
hold on;
x1=fzero(@funcy,-6);
x2=fzero(@funcy,6);
scatter(x1,x1^2,'r');
...