Pre-U
Pre-U 9795/1
2010
June
Q1
4 marks
Standard +0.8
1 The equation \(x ^ { 3 } + 2 x ^ { 2 } + x - 7 = 0\) has roots \(\alpha , \beta\) and \(\gamma\). Use the substitution \(y = 1 + x ^ { 2 }\) to find an equation, with integer coefficients, whose roots are \(1 + \alpha ^ { 2 } , 1 + \beta ^ { 2 }\) and \(1 + \gamma ^ { 2 }\).
Pre-U
Pre-U 9795/1
2012
June
Q13
6 marks
Challenging +1.8
13 Define the repunit number, \(R _ { n }\), to be the positive integer which consists of a string of \(n 1\) 's. Thus,
$$R _ { 1 } = 1 , \quad R _ { 2 } = 11 , \quad R _ { 3 } = 111 , \quad \ldots , \quad R _ { 7 } = 1111111 , \quad \ldots , \text { etc. }$$
Use induction to prove that, for all integers \(n \geqslant 5\), the number
$$13579 \times R _ { n }$$
contains a string of ( \(n - 4\) ) consecutive 7's.