Posted by **jane** on Tuesday, November 25, 2008 at 8:16pm.

Definition of the derivative to calculate f'(x) if f(x) = square root 2x. Find the equation of the tangent & normal line to the graph of f at x=2.

Tangent line - y=2x-x

Normal line - y = 1/2x +3

I do not know whether these are the correct answers.

- HS Calculus -
**Reiny**, Tuesday, November 25, 2008 at 9:24pm
no.

y = √(2x) = (2x)^(1/2)

y' = (1/2)(2x)^(-1/2)(2) = 1/√(2x)

when x=2, y = 2, y' = 1/2

so the tangent line is

y = (1/2)x + b

which at (2,2) is 2 = (1/2)(2) + b

b = 1

so the tangent equation is y = (1/2)x + 1

the normal would have slope of -2

so at (2,2)

2 = -2(2) + b

b = 6

the normal has equation y = -2x + 6

- HS Calculus -
**jane**, Tuesday, November 25, 2008 at 9:50pm
Thank you . I think that I understand alittle better. It is oblivious that I do not understand this material.

- HS Calculus -
**jane**, Tuesday, November 25, 2008 at 9:53pm
I have one more that I really am lost at.

Question - find the points on the graph y=2x^3-3x^2-12x+20 at which the tangent is parallel to tthe x-axis. I do not even know where to begin. We were told we could use the shortcut for this one.!

Thanks again

- HS Calculus -
**Reiny**, Tuesday, November 25, 2008 at 10:17pm
If a tangent is parallel to the x-axis, wouldn't it have a slope of zero?

And isn't the slope represented by the first derivative?

so differentiate, set that equal to zero and solve for x

find the y's for those x's and simply say

y = (whatever the y values are)

let me know if you don't get y = 0 and y = 27

## Answer This Question

## Related Questions

- calculus - use the definition of the derivative to calculate f'(x), if f(x)= ...
- Calculus - find the equation of a line tangent to the graph of y = x / (square ...
- Calculus - If F(x)=x^3−7x+5, use the limit definition of the derivative to...
- calculus - 1. Which of the following expressions is the definition of the ...
- calculus - 1. Which of the following expressions is the definition of the ...
- calculus - Find an equation of the line that is tangent to the graph f and ...
- Calculus - The function g is defined for x>0 with g(1)=2, g'(x)=sin(x+1/x), ...
- cal - find the equation of a quadratic function whose graph is tangent at x=1 to...
- College Calculus - Let f(x) = 3x^2 - 2x + 1 a) write an equation of the line ...
- Calculus-math - Find an equation of the line that is tangent tothe graph of f ...

More Related Questions