MTH107 Problem Sheet 1 (Week 1 2021/22)
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MTH107 Problem Sheet 1 (Week 1 2021/22)
Tutorial questions
1. Let X = {a} and Y = {b, c}.
List all possible functions from X to Y (you may draw a diagram).
List all functions from Y to X .
Compose a function from the first list with a function from the second list (in either order). What
are all the different functions that arise in this way?
2. Let X ,Y , Z be sets and suppose that f : X → Y and g : Y → Z are functions. Show that if f and g are injective then g ∘ f is injective.
Show that if f and g are surjective then g ∘ f is surjective.
If g ∘ f is injective then what can you say about f or g? What if g ∘ f is surjective?
3. Recall that F stands for R or C. Prove that Fn satisfies the distributive properties, that is, for all a, b ∈ F and u,v ∈ Fn we have:
a(u + v) = au + av ,
(a + b)v = av + bv .
The identity map on a set X is the function idX : X → X given by idX (x) = x for all x ∈ X .
4. Let f : X → Y and g : Y → X be functions. Suppose that g ∘ f = idX . Does it follow that f ∘ g = idY ?
Further questions
5. Let X and Y be finite sets and f : X → Y be a function.
Assume that f is injective. Find a function g : Y → X such that g ∘ f = idX .
Assume that f is surjective. Find a function g : Y → X such that f ∘ g = idY . The following questions are intended as revision for some Year 1 Linear Algebra.
6. Solve the system of linear equations
x1 + 3x2 − 5x3 = 4
x1 + 4x2 − 8x3 = 7
−3x1 − 7x2 + 9x3 = −6.
7. Let A = ⎡ ⎤ . Find detA and A−1 .
⎣ −1 3 4 ⎦
2022-07-30