# Find the Lines that are tangent and normal to curve at given point.

• Nov 12th 2009, 01:46 PM
Cyberman86
Find the Lines that are tangent and normal to curve at given point.
Find the Lines that are Tangent and Normal to the Curve at the given points.

x^2+xy-y^2 = 11 , (3,1)

a) Give the equation that is tangent to the curve.
2x+(x dy/x + y dy/x) - 2y dy/dx = 0
(x-2y)dy/dx + 2x+y = 0
(x-2y)dy/dx = -2x-y
dy/dx = -2x-y/x-2y

dy/dx= -2(3)-1 / 3-2(1) = 7/1

y= y1 + m(x-x1)
y= 1 + 7/1(x-3) = ??? (I have tried many problems like this in Mymathlab and always get wrong this part)

b) Give the Equation that is Normal to the Curve.

y=1-7/1(x-3)

y= (also can't get this part right)

Please if Someone can show step by step how to do this problem I will appreciated.
• Nov 12th 2009, 02:35 PM
Plato
Quote:

Originally Posted by Cyberman86
Find the Lines that are Tangent and Normal to the Curve at the given points.

x^2+xy-y^2 = 11 , (3,1)

If $m\ne 0$ is the slope of the curve at $(p,q)$ on the curve:
The tangent is $y-q=m(x-p)$ and the normal is $y-q=\frac{-1}{m}(x-p).$