The curve C has parametric equations $x = 2t - \dfrac{1}{t^{2}},\quad y = 2t + \dfrac{1}{t},\quad t \in \mathbb{R},\ t \ne 0. The point P on the curve has parameter .
- (i)
Find the equation of tangent and normal to C at the point P.
- (ii)
The tangent at P meets the y-axis at B. The normal at P meets the x-axis at A. If O is the origin, find the area of the quadrilateral OAPB.
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Worked solution
3(i)
1. Find the coordinates of $P$ by substituting $t = 1$ into the parametric equations.
The coordinates of are .
2. Differentiate $x$ and $y$ with respect to $t$ and evaluate them at $t = 1$.
At ,
At ,
3. Calculate the gradient of the tangent, $\frac{dy}{dx}$, at point $P$.
Using the chain rule for parametric equations:
The gradient of the tangent at is .
4. Form the equations of the tangent and the normal.
Equation of the tangent (gradient ):
Gradient of the normal is .
Equation of the normal:
Tangent: , Normal:
3(ii)
1. Find the coordinates of P and the gradient of the curve at $t=1$ (derived from part i).
At , and . Thus is .
At , and .
2. Form equations of the tangent and normal to find the coordinates of points A and B (derived from part i).
Equation of the tangent at :
The tangent meets the -axis () at , so . Thus, .
Equation of the normal at :
The normal meets the -axis () at , so . Thus, .
3. Calculate the area of quadrilateral OAPB.
The coordinates are , , , and .
Using the shoelace (array) method to find the area of the polygon:
4
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