tangent line to y = 2x^2 - 1 through (4, 13)

[orangecrush]

Find the equation of the line(s) through the point (4, 13) that is/are tangent to the parabola y = 2x^2 - 1.

I think I got one line, y = 4x - 3, but I don't think the way I got it is the way you're supposed to get it. It's something about slopes of the lines and the parabola.

 

[stapel]

I got it is the way you're supposed to get it.

How did you get it, then? (Yes, you're supposed to use slopes and such.)

Please be specific. Thank you.

Eliz.

 

[orangecrush]

the slope for y=2x^2-1 is y'=4x. so, y-13=4x(x-3) and I solved it which gets y=4x^2-3 which has a square in it but i graphed y=4x-3 anyways cause i was desperate and it looks like a right answer but yeah, i did it wrong. so i'd like to know the right way.

 

[orangecrush]

so is y=4x-3 the right way, and is there another equation also?