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 10
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
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To find the gradient at point P(1, 4), substitute x = 1 into the gradient equation:
dxdy=(3(1)−1)2=(3−1)2=22=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=−41.
Using the point-slope form of a line, the equation of the normal at P can be written as:
(y−4)=−41(x−1).
Rearranging gives:
y−4=−41x+41,
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
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Starting from the gradient equation:
dxdy=(3x−1)2,
we integrate to find y:
y=∫(3x−1)2dx.
To integrate, we expand the square:
(3x−1)2=9x2−6x+1.
Integrating term-by-term gives:
y=∫(9x2−6x+1)dx=39x3−26x2+x+C=3x3−3x2+x+C.
Now, substituting the point (1, 4) to find C:
4=3(1)3−3(1)2+1+C,
which simplifies to:
4=3−3+1+CC=0.
Thus, the equation of the curve C is:
y=3x3−3x2+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
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The gradient of the line y = 1 - 2x is -2. For the tangent to be parallel to this line, we must have:
dxdy=−2.
Setting the gradient of the curve equal to -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.