Question 1039547
<pre>
Sorry, but they're both wrong.

The "4 if {{{x<=-1}}}" tells us that the circle at (-1,4)
is included and therefore should be darkened "&#9679;" and the 
"-4 if {{{x>-1}}}" tells us that the circle at (-1,-4) is 
not included and should be open "o".

And in the other problem negative infinity is always written
left of infinity.
This: {{{(matrix(1,3,-infinity,",",infinity))}}}, not this: {{{cross((matrix(1,3,infinity,",",-infinity)))}}} 
Edwin</pre>