MAT 150C University of California Davis Modern Algebra Questions Answers please write the answer and logic clearlyhope nice writinghere is the hw and hando

MAT 150C University of California Davis Modern Algebra Questions Answers please write the answer and logic clearlyhope nice writinghere is the hw and handout MAT 150C: MODERN ALGEBRA
Homework 3
Instructions. Please write the answer to each problem, including the computational ones, in connected
sentences and explain your work. Just the answer (correct or not) is not enough. Write your name in every
page and upload to Gradescope with the correct orientation. Make sure to indicate to Gradescope which
pages correspond to each problen.
1. Recall that SL2 (C) is the group of all 2 × 2 complex matrices with determinant 1. In this problem, we
will show that SL2 (C) has the structure of an irreducible algebraic variety.
(a) Let f (x, y) = x2 + y 2 − 1 ∈ C[x, y]. Show that V (f ) does not contain any line of the form
L = V (ax + by + c). Conclude that f is irreducible.
(b) Now let g(x, y, z, w) = xy − zw − 1 ∈ C[x, y, z, w]. Use part (a) to show that g is irreducible.
Explain why this implies that SL2 (C) is an irreducible algebraic variety.
(c) Show that h(x, y, z, w) = xy − zw ∈ C[x, y, z, w] is irreducible. (Note: this does not follow
immediately from (b))
2. Let m ∈ Z be a square-free number (meaning that no square divides m). Show that xn −m is irreducible
in Q[x] for every n ≥ 1.
3. For n > 0, denote
n
e n (x) := x − 1 = xn−1 + xn−2 + · · · + x + 1 ∈ Z[x]
Φ
x−1
e p (x) is irreducible in Z[x] (equivalently, in Q[x]).
we have seen in class that if p is prime, then Φ
e m (x) divides Φ
e n (x) in Z[x].
(a) Assume m divides n. Show that Φ
e n (x) is irreducible in Z[x] if and only if n is prime.
(b) Conclude that Φ
e 2p (x) into irreducible factors in Z[x].
(c) Let p be an odd prime number. Decompose Φ
e n (x)
In general, we define the n-th cyclotomic polynomial Φn (x) inductively as follows. Decompose Φ
into irreducible, monic polynomials in Z[x]. One of this factors is not equal to Φm (x) for m