用Mathematica解方程组,输出如下错误,何意?另考虑到是否为无解,请问用该软怎么判断方程组是否有解?

用Mathematica解方程组,输出如下错误,何意?另考虑到是否为无解,请问用该软怎么判断方程组是否有解?
输入Solve[(y1 - y2)/(x1 - x2) = (55 - 16)/(-8 -
13),(x1 - x2)^2 + (y1 - y2)^2 = (55 - 16)^2 + (-8 -
13)^2,(x2 - 5)^2 + (y2 - 10)^2 = (13 - 5)^2 + (16 -
10)^2,(x1 - 5)^2 + (y1 - 10)^2 = (-8 - 5)^2 + (55 - 10)^2,{x1,
x2,y1,y2}]
输出Set::write:Tag Times in (y1-y2)/(x1-x2) is Protected.>>
Set::write:Tag Plus in (x1-x2)^2+(y1-y2)^2 is Protected.>>
Set::write:Tag Plus in (-5+x2)^2+(-10+y2)^2 is Protected.>>
General::stop:Further output of Set::write will be suppressed during this calculation.>>
Solve::nonopt:Options expected (instead of {x1,x2,y1,y2}) beyond position 4 in Solve[-(13/7),1962,100,2194,{x1,x2,y1,y2}].An option must be a rule or a list of rules.>>
上面的输入出错误了，少了一个“=”。
输入改正为下：Solve[(y1 - y2)/(x1 - x2) == (55 - 16)/(-8 -
13),(x1 - x2)^2 + (y1 - y2)^2 == (55 - 16)^2 + (-8 -
13)^2,(x2 - 5)^2 + (y2 - 10)^2 == (13 - 5)^2 + (16 -
10)^2,(x1 - 5)^2 + (y1 - 10)^2 == (-8 - 5)^2 + (55 -
10)^2,{x1,x2,y1,y2}]
输出为：Solve::nonopt:Options expected (instead of {x1,x2,y1,y2}) beyond position 4 in Solve[(y1-y2)/(x1-x2)==-(13/7),(x1-x2)^2+(y1-y2)^2==1962,(-5+x2)^2+(-10+y2)^2==100,(-5+x1)^2+(-10+y1)^2==2194,{x1,x2,y1,y2}].An option must be a rule or a list of rules.>>
输出提示为何意？用何种方法判断方程组是否有解？急...

所有的关系方程必须用{ }括起来,正确的为：
Solve[{(y1 - y2)/(x1 - x2) == (55 - 16)/(-8 -
13),(x1 - x2)^2 + (y1 - y2)^2 == (55 - 16)^2 + (-8 -
13)^2,(x2 - 5)^2 + (y2 - 10)^2 == (13 - 5)^2 + (16 -
10)^2,(x1 - 5)^2 + (y1 - 10)^2 == (-8 - 5)^2 + (55 -
10)^2},{x1,x2,y1,y2}]
解出来有两组解,运行结果为：
{{x1 -> 18,x2 -> -3,y1 -> -35,y2 -> 4},{x1 -> 3860/109,x2 -> 1571/109,y1 -> (2793/109),
y2 -> 1458/109},
{x1 -> -(2770/109),x2 -> -(481/109),y1 -> 4973/109,y2 -> 722/109},{x1 -> -8,x2 -> 13,y1 -> 55,y2 -> 16}}
可以给积分了吧!