308 Rings 252 29. Suppose that a and b belong to a commutative ring R with unity. If 30. Suppose that there is an integer n> 1 such that x" x of some ring. If m is a positive integer x for all elements a is a unit of R and b2 0, show that a + b is a unit of R. O for some a, show and a" 0. that a 31. Give an example of ring elements a and b with the properties that ab 0 but ba 0. х, 32. Let n be an integer greater than 1. In a ring in which x" = x for all 0. 0 implies ba show that ab 33. Suppose that R is a ring such that x3 = x for allx in R. Prove that 0 for all x in R бх = a. Prove that a2n a2 34. Suppose that a belongs to a ring and a for all n 1. = a for all a in Z. Do the same 6 35. Find an integer n > 1 such that a" for Zo Show that no such n exists for Z when m is divisible by the 10 т of some prime. square 36. Let m and n be positive integers and letk be the least common mul- tiple of m and n. Show that mZn nZ kZ. 37. Explain why every subgroup of Z, under addition is also a subring of Zg 38. Is Z a subring of Z,? 39. Suppose that R is a ring with unity 1 and a is an element of R such that a2 = 1. Let S Co ara l rE R}. Prove that S is a subring of R. Does S contain 1? 40. Let M,(Z) be the ring of all 2 X 2 matrices over the integers and let R = {, ;]z} 4.bEZ a + b a Prove or disprove that R is a subring a +b b of M2(Z). 41. Let M2(Z) be the ring of all 2 X 2 matrices over the integers and let R S а a a, bE Z. Prove or disprove that R is a subring a -b b of M(Z). 42. Let R a Prove or disprove that R is a subring b of M,(Z). 43. Let R Zze Z and S {(a, b, c) E Rla+ b = c}. Prove or disprove that S is a subring of R. 44. Suppose that there is a positive even integer n such that a" = a for all elements a of some ring. Show that -a a for all a in the ring.
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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