Posted by **Anonymous** on Thursday, February 28, 2013 at 9:19pm.

Determine the coordinates of the point on the graph of f(x)= (2x+1)^(1/2) where the tangent line is perpendicular to the line 3x+y+4=0

- calculus -
**Reiny**, Thursday, February 28, 2013 at 10:36pm
dy/dx = (1/2) (2x+1)^(-1/2) (2)

= 1/(2x+1)^(1/2) or 1/√(2x+1)

slope of line is -3

so slope of perpendicular is 1/3

so we have ...

1/√(2x+1) = 1/3

√(2x+1) = 3

square both sides ...

2x + 1 = 9

2x = 8

x = 4

f(4) = (9)^1/2) = 3

so the point of contact is (4,3)

and the equation of the tangent is

y-3 = (1/3)(x-4)

3y - 9 = x-4

x - 3y = -5 OR y = (1/3)x + 5/3

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