Past Papers’ Solutions  Edexcel  AS & A level  Mathematics  Core Mathematics 1 (C16663/01)  Year 2017  June  Q#9
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Question
a. On separate axes sketch the graphs of
i. y = –3x + c, where c is a positive constant,
ii.
On each sketch show the coordinates of any point at which the graph crosses the
yaxis and the equation of any horizontal asymptote.
Given that y = –3x + c, where c is a positive constant, meets the curve at two distinct points,
b. show that (5 – c)^{2} >12
c. Hence find the range of possible values for c.
Solution
a.
We are required to sketch a line and a curve.
i.
First we sketch the line.
We are given equation of the line as;
First we find the xintercept of the line.
The point at which curve (or line) intercepts xaxis, the value of . So we can find the value of coordinate by substituting in the equation of the curve (or line).
Therefore, we substitute in equation of the line.
Hence, coordinates of xintercept of the line are .
Next, we find the yintercept of the line.
The point at which curve (or line) intercepts yaxis, the value of . So we can find the value of coordinate by substituting in the equation of the curve (or line).
Therefore, we substitute in equation of the line.
Hence, coordinates of yintercept of the line are .
We can sketch the line as shown below.
ii.
We are required to sketch the graph and given that;
It may be a lot easier to first sketch;
A graph of the form is known as a reciprocal graph and looks like;
We have the sketch of the curve with equation .
We are required to sketch y=f(x)+5.
Translation through vector represents the move, units in the xdirection and units in the positive ydirection.
Translation through vector transforms the function into or .
Transformation of the function into or results from translation through vector .
Translation vector transforms the function into or which means shift upwards along yaxis.
Original 
Transformed 
Translation Vector 
Movement 

Function 



units in 
Coordinates 


It is evident that y=f(x)+5 is a case of translation by 5 units along positive yaxis.
Next we are required to state the equations of asymptotes.
An asymptote is a line that a curve approaches, as it heads towards infinity. Both horizontal and vertical asymptotes may exist for a given graph. The distance between the curve and the symptote tends to zero as they head to infinity.
For the graph sketched above, we can draw horizontal and vertical asymptotes as shown below.
It is evident that horizontal asymptote (orange line) can be stated with equation;
Similarly, vertical asymptote (blue line) is yaxis and can be stated with equation;
b.
We are given that y = –3x + c, where c is a positive constant, meets the curve at two distinct points, therefore, the line and the curve intersect at two distinct point.
If two lines (or a line and a curve) intersect each other at a point then that point lies on both lines i.e. coordinates of that point have same values on both lines (or on the line and the curve). Therefore, we can equate coordinates of both lines i.e. equate equations of both the lines (or the line and the curve).
Equation of the line is;
Equation of the curve is;
Equating both equations;
Two values of x indicate that there are two intersection points.
Since we are given that the line and the curve intersect at two distinct points, this quadratic equation must have two distinct roots.
For a quadratic equation , the expression for solution is;
Where is called discriminant.
If , the equation will have two distinct roots.
If , the equation will have two identical/repeated roots.
If , the equation will have no roots.
Therefore, for this quadratic equation;
c.
We are required to solve the inequality;
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