Finding equation of a Tangent Line
Find an equation of the line that is tangent to the graph of f and parallel to the given line.
Function: f(x) = 2x^2
Line: 4x – y + 4 = 0
Tell me what I'm doing wrong. According to my instructor's directions:
Step 1. Find the slope of the tangent line:
Do the algebra, reduces to 4x-2h - the limit/slope is 4x.
Step 2. Find the slope of the given line:
4x – y + 4 = 0 same as y=4x+4 and so m=4
Step 3. Set the slope of the tangent equal to the slope of the given line, and solve for x.
4x=4 so x=1
Step 4. Use the values from above to find the equation of the line.
(So elsewhere in the lecture, he mentions that if x=1, then your reference point is (1,1) - if someone else can explain why, I'd appreciate that too. I'm not getting that. But assuming that it is....)
Why isn't this right? What am I missing? I'm sure it's something obvious and dumb?