MATHS 120 Algebra SEMESTER ONE, 2022
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SEMESTER ONE, 2022
MATHS 120
MATHEMATICS
Algebra
1. Let n 2 N,n 0:
(a) Show that < . (1 mark)
(b) Show that = − . (1 mark)
(c) Use (a) and (b) to show by induction that Pk(n)=1 < 2 − . (3 marks)
2. Let X = {1, 2, 3} and Y = {a,b,c,d}.
(a) How many surjective functions are there from X to Y? (3 marks)
(b) How many injective functions are there from X to Y? (2 marks)
3. Let f : Z2 ! Z2 be given by f(a,b) = (a + b,a − b). Is f surjective? (7 marks)
4. Find all complex numbers z such that |z − i| = |z + i|. What object do they represent in the complex plane? (3 marks)
5. Two planes ⇡1 and ⇡2 in R3 are called parallel if every normal vector to ⇡1 is also a normal vector to ⇡2 and every normal vector to ⇡2 is a normal vector to ⇡1 .
Show that if ⇡1 and ⇡2 are parallel and ax+by +cz +d = 0 is a Cartesian equation for ⇡1 then there exists e 2 R such that ax + by + cz + e = 0 is a Cartesian equation for ⇡2 . (5 marks)
6. Let f : R3 ! R3 be the linear transformation which is projection onto the XY-plane. Let g : R3 ! R3 be a counterclockwise rotation about the Z-axis over an angle .
(a) What is the matrix corresponding to g ◦ f? (2 marks)
(b) If g ◦ f invertible? (1 mark)
(c) Is g ◦ f = f ◦ g? (2 marks)
7. Let B1 = {v1 , . . . ,vn} and B2 = {w1 , . . . ,wn} be two bases for Rn . By Proposition 2.3.9. in the coursebook there exists a unique linear transformation T : Rn ! Rn such that T(vi) = wi , Ai 2 {1, ··· ,n}. What is (if it exists) the inverse of T? (4 marks)
8. For which value(s) of a is the determinant of 26(3)
42
2
8
−2
4 5 equal to zero? (6 marks)
2022-10-19