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0 | S o l u t i o n b y F a j a r S . H a r s a

CAMBRIDGE INTERNATIONAL EXAMINATION

QUESTIONS (ADVANCE SUBSIDIARY AND ADVANCE

LEVEL : PURE MATHEMATICS ) 2018

(Solution by Fajar S. Harsa)

PART 1 (PROBLEM OF THE MONTH)

Question 1 6

1 |Solution by Fajar S. Harsa

1. The coefficient of in the expansion of 

is 330. Find the value of

the constant

Solution

With binomial newton, we get :



Then,







 

   

  

 



2 |Solution by Fajar S. Harsa

2. The equation of a curve is , where

is a constant

(i) Find set of values of  for which the whole of the curve lies above the

x-axis

(ii) Find the value of for which the line  is a tangent to the curve

Solution

(i) If a curve lies above the

x-axis

, then the equation of a curve must have

discriminant less than 0 or has no real x solution.

So, The discriminant of the equation  with  

 ; 

  

  





The curve lies above the

x-axis ,

when 

(ii) Slope of tangent line to the curve   at point  , is

derivative of  or  . Suppose the line  which has

slope is a tangent to the curve at point  , , so ;

   





Because point  , lies on line  and also curve  ,

so :  



 





The value of for which the line  is a tangent to the curve is 5

3 |Solution by Fajar S. Harsa

3. A company producing salt from sea water changed to a new process. The amount of

salt obtained each week increased by 2% of the amount obtained in preceding week.

It is given that in the first week after the change the company obtained 8000 kg of

salt.

(i) Find the amount of salt obtained in the 12th week after the change.

(ii) Find the total amount of salt obtained in the first 12 weeks after the change

Solution

Suppose , amount of salt in -th week

(i) Week 1 : 

Week 2 :  

Week 3 :    

Week 4 :    

By seeing the pattern , we conclude :  

So, in 12th week, amount of salt is      

(ii) Total amount of salt obtained in the first 12 weeks after the change (S)



   

     

 



   

 

So, the total amount of salt obtained in the first 12 weeks after the change is



4 |Solution by Fajar S. Harsa

4. The function  is such that  . It is given that

 and  .

(i) Find the values of the constant 

(ii) Find the set of values of

k

for which the equation has no solution

Solution

(i)  , then :

    

     

By eliminating (1) and (2) , we get 

(ii) If , then   and we get  

 .

 must be less than 1 or greater than 1 in order to get the value of which

the equation  has no solution .



  



 

 

5 |Solution by Fajar S. Harsa

5.

The diagram shows a three-dimensional shape. The base OAB is a horizontal triangle

in which angle AOB is 90o. The side OBCD is a rectangle and the side OAD lies in a

vertical plane. Unit vectors I and j are parallel to OA and OB respectively and the unit

vector k is vertical. The position vectors of A, B, and D are given by 

 .

(i) Express each the vectors 

in terms of  and

(ii) Use a scalar product to find angle CAD

Solution

(i)



6 |Solution by Fajar S. Harsa





   

(ii) 

  

Suppose  , the scalar product :





      

    

 

 

 

7 |Solution by Fajar S. Harsa

6.

The diagram shows points A and B on a circle with centre O and radius r. The tangents

to the circle at A and B meet at T. The shaded region is bounded by the minor arc AB

and the lines AT and BT. Angle AOB is  radians

(i) In the case where the area of the sector AOB is the same as the area of the

shaded region, show that than  

(ii) In the case where  and the length of the minor arc AB is 19.2 cm, find

the area of the blue region

Solution

(i)

 

  



  

    



8 |Solution by Fajar S. Harsa



 





 

 (Proved)

(ii) The minor arc AB is 19.2 cm and  , then :

   

 



 

 

  

 

   cm2

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