Okay. Here goes... Thanks in advance to anyone who can help.
Find the range of values of c for which the straight line y=3x+c intersects the curve in 2 distinct points
so this is how i did it (and it was all right, according to the answers- ill bold the part that i don't get why you do)
(because 2 distinct points)
OK, AND THIS IS THE LAST PART, BUT I HAVE NO CLUE HOW( OR WHY ITS DONE) TO GET THIS