Quick C4 parametric equation question, help please!!

A curve is given parametrically by the equations

x = t^2 y= 1/t

a) find dy/dx in terms of t, giving your answer in its simplest form.

when i try to do this i get a different answer to the mark scheme i diff 1/t to get ln t but thats wrong?

b)show the equation of the tangent at the point P (4, -1/2) IS

x - 16y =12.

c) Find the value of the parameter where the tangent at P meets the curve again

Reply 1

remember

you don't need to integrate, differentiate

Reply 2

topcrabcakes

a) dy/dx = (dy/dt) * 1/(dx/dt)
= -1/(t^2) * 1/(2t)
= -1/(2t^3)

b) simultaneous equations to find t: x=4,y=-1/2

then plug into our dy/dx and then put into tangent equation.

etc etc

Reply 3

jakezg

rayman198

A curve is given parametrically by the equations

x = t^2 y= 1/t

a) find dy/dx in terms of t, giving your answer in its simplest form.

when i try to do this i get a different answer to the mark scheme i integrate 1/t to get ln t but thats wrong?

b)show the equation of the tangent at the point P (4, -1/2) IS

x - 16y =12.

c) Find the value of the parameter where the tangent at P meets the curve again

Part A)is all about differentiation not integration. You do Dx/dt= 2t and dy/dt= -1/t^2.. then u do dy/dt / dx/dt..

Sub in the points to get the gradient for B and then do the y-y1=m(x-x1) formula.