A curve C has the following equation: x^3 + 3y - 4(x^3)*(y^3) a) Show that (1,1) lies on C b) Find dy/dx

a) Substituting the coordinate (1,1) into the left hand side of the equation for C we obtain: (13) + 3*1 - 4(13)(13) = 1 + 3 - 4 = 0 = The right hand side of the equation, hence the equation is satisfied, and therefore (1,1) lies on C.

b) Differentiating implicity we find: 
3x2 + 3dy/dx - 12x2y3 - 12x3y2dy/dx = 0
Rearranging yields:
3x2 - 12x2y3= (12x3y2 - 3)dy/dx

Hence dy/dx = (3x2 - 12x2y3/(12x3y2 - 3)
Which simplifies to 

dy/dx = x2(1 - 4y3)/(4x3y2 - 1)

(An alternative expression can be obtained be moving the terms not involving dy/dx to the right hand side)

HW

Related Maths A Level answers

All answers ▸

The curve A (y = x3 – x2 + x -1) is perpendicular to the straight-line B at the point P (5, 2). If A and B intersect at P, what is the equation of B? Also, find any stationary points of the curve A.


How do you factorise quadratic, cubic functions or even quartic functions?


Find both stationary points for y= 4x^(3)-3x^(2)-60x+24. Also find the nature of those points.


What is differentiation?