Equation for intersecting tangent lines

[dcowboys107]

Write equations for the two straight lines that pass through the poing (2,5) and are tangent to the parabola y=4x-x^2.

 

I drew the figure and the lines. I fought the slope for the tangent lines (2 and -2) and eventually the equations y=-2x+9 and y=2x+1

 

When I plugged the three equations into my calcuator to see if I was right it seems that I was off on y=-2x+9, that it doesn't reach 5 when x is two but at 4. The second one seems right.

 

Am I right and the calcultar be wrong? Thanks.

[DJBruce]

Did you try checking your math by hand?

[dcowboys107]

I think I got it to work. Does that seem like the right answer though?

[DJBruce]

It looks like it, and when I checked it by hand and calculator it seemed to work. So I am assuming you must have just entered something improperly into your calculator. (Ergo why I asked you to check it manually.)