238 Groups Supplementary Exercises for Chapters 9-11 Every prospector drills many a dry hole, pulls out his rig, and moves on JOHN L. HESS True/false questions for Chapters 9-11 are available on the Web at: http://www.d.umn.edu/~jgallian/TF 1. Suppose that H is a subgroup of G and that each left coset of H G is some right coset of H in G. Prove that H is normal in G. 2. Use a factor group-induction argument to prove that a finite group of order n has a subgroup of order m for Abelian tive divisor m of n. every posi- 3. Let diag(G) = {(g, g) | g E G}. Prove that diag(G) GGif and only if G is Abelian. When G is finite, what is the index of diag(G) in G G? 4. Let H be any group of rotations in D. Prove that H is normal in D 5. Prove that Inn(G) Aut(G) n' n2 6. Let H be a subgroup of G. Prove that H is a normal subgroup if and only if, for alla and b in G, ab E H implies ba E H. 7. The factor group GL(2, R)/SL(2, R) is isomorphic to some very familiar group. What is the group? 8. Let k be a divisor of n. The factor group (Z(n))/((k)/(n)) is isomor phic to some very familiar group. What is the group? 9. Let а a, b, c E Q 0 1 Н — с 0 0 under matrix multiplication. a. Find Z(H). b. Prove that Z(H) is isomorphic to Q under addition. c. Prove that H/Z(H) is isomorphic to Q Q. d. Are your proofs for parts a and b valid when Q is replaced by R? Are they valid when Q is replaced by Z, where p is prime? 10. Prove that DIZ(D,) is isomorphic to Z, Z2. 11. Prove that Q/Z under addition is an infinite group in which every element has finite order. 12. Show that the intersection of any collection of normal subgroups of a group is a normal subgroup.
Angles in Circles
Angles within a circle are feasible to create with the help of different properties of the circle such as radii, tangents, and chords. The radius is the distance from the center of the circle to the circumference of the circle. A tangent is a line made perpendicular to the radius through its endpoint placed on the circle as well as the line drawn at right angles to a tangent across the point of contact when the circle passes through the center of the circle. The chord is a line segment with its endpoints on the circle. A secant line or secant is the infinite extension of the chord.
Arcs in Circles
A circular arc is the arc of a circle formed by two distinct points. It is a section or segment of the circumference of a circle. A straight line passing through the center connecting the two distinct ends of the arc is termed a semi-circular arc.
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