Photo AI

The gradient of the curve C is given by dy/dx = (3x - 1)² - Edexcel - A-Level Maths Pure - Question 10 - 2005 - Paper 2

Question icon

Question 10

The-gradient-of-the-curve-C-is-given-by--dy/dx-=-(3x---1)²-Edexcel-A-Level Maths Pure-Question 10-2005-Paper 2.png

The gradient of the curve C is given by dy/dx = (3x - 1)². The point P(1, 4) lies on C. (a) Find an equation of the normal to C at P. (b) Find an equation for th... show full transcript

Worked Solution & Example Answer:The gradient of the curve C is given by dy/dx = (3x - 1)² - Edexcel - A-Level Maths Pure - Question 10 - 2005 - Paper 2

Step 1

Find an equation of the normal to C at P.

96%

114 rated

Answer

To find the gradient at point P(1, 4), substitute x = 1 into the gradient equation:

dydx=(3(1)1)2=(31)2=22=4.\frac{dy}{dx} = (3(1) - 1)^{2} = (3 - 1)^{2} = 2^{2} = 4.

The gradient of the normal is the negative reciprocal of the gradient of the tangent. Therefore, the gradient of the normal is:

Gradient of normal=14.\text{Gradient of normal} = -\frac{1}{4}.

Using the point-slope form of a line, the equation of the normal at P can be written as:

(y4)=14(x1).(y - 4) = -\frac{1}{4}(x - 1).

Rearranging gives:

y4=14x+14,y - 4 = -\frac{1}{4}x + \frac{1}{4},

y = -\frac{1}{4}x + \frac{17}{4}.

Step 2

Find an equation for the curve C in the form y = f(x).

99%

104 rated

Answer

Starting from the gradient equation:

dydx=(3x1)2,\frac{dy}{dx} = (3x - 1)^{2},

we integrate to find y:

y=(3x1)2dx.y = \int (3x - 1)^{2}dx.

To integrate, we expand the square:

(3x1)2=9x26x+1.(3x - 1)^{2} = 9x^{2} - 6x + 1.

Integrating term-by-term gives:

y=(9x26x+1)dx=93x362x2+x+C=3x33x2+x+C.y = \int (9x^{2} - 6x + 1)dx = \frac{9}{3}x^{3} - \frac{6}{2}x^{2} + x + C = 3x^{3} - 3x^{2} + x + C.

Now, substituting the point (1, 4) to find C:

4=3(1)33(1)2+1+C,4 = 3(1)^{3} - 3(1)^{2} + 1 + C,

which simplifies to:

4=33+1+C C=0.4 = 3 - 3 + 1 + C \ C = 0.

Thus, the equation of the curve C is:

y=3x33x2+x.y = 3x^{3} - 3x^{2} + x.

Step 3

Using dy/dx = (3x - 1)², show that there is no point on C at which the tangent is parallel to the line y = 1 - 2x.

96%

101 rated

Answer

The gradient of the line y = 1 - 2x is -2. For the tangent to be parallel to this line, we must have:

dydx=2.\frac{dy}{dx} = -2.

Setting the gradient of the curve equal to -2:

(3x1)2=2.(3x - 1)^{2} = -2.

Since the left-hand side (a square) is always non-negative, it cannot equal -2. Hence, there is no point on C where the tangent is parallel to the line y = 1 - 2x.

Join the A-Level students using SimpleStudy...

97% of Students

Report Improved Results

98% of Students

Recommend to friends

100,000+

Students Supported

1 Million+

Questions answered

;