(c) Let G3 be the set of all nonconstant functions from R to R of the form f(r) = ax +b where a is a nonzero real number and b can be any real number. Prove or disprove: G3 is a group under composition. (d) Let G4 be the set of all functions from R to R of the form f(x) ar³,where a is a nonzero real number. Prove or disprove: G4 is a group under composition. %3D

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Chapter2: Second-order Linear Odes
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Please do exercise 8.8.4 and do part c and d and please show step by step and explain

Proposition 8.8.3. Let A be a set, and let G be the set of all invertible
functions from A to A. Then G is a group under composition.
In the following exercise we look at some particular sets of functions, and
investigate whether or not these sets form groups under composition. Recall
that to show whether or not a set with binary operation is a group, you just
need to show the properties: closure, identity, inverse, and associative. We're
lucky in this case that we don't have to prove associative in every single case,
because the operation of function composition is always associative, as we've
proven before. So it's enough just to prove closure, identity, and inverse.
Exercise 8.8.4.
(a) Let G1 be the set of all nonzero functions from R to R of the form
= ax, where a is a nonzero real number. (For example, the func-
tions g(r) = -7x and h(x) = v2x are both elements of G1.) Prove
or disprove: G1 is a group under composition. (Note: G1 is the set of
nonzero linear functions from R to R.)
(b) Let G2 be the set of all nonzero functions from R to R of the form
f(x)
zero. (For example, the functions p(x) = 29.4x + 42.3, q(x) = 15 and
r(x) = -nx are all elements of G2.) Prove or disprove: G2 is a group
under composition. (Note: G2 is called the set of all nonzero affine
functions from R to R.)
= ax + b where a and b are real numbers which are not both
(c) Let G3 be the set of all nonconstant functions from R to R of the form
f(r)
= ax + b where a is a nonzero real number and b can be any real
number. Prove or disprove: G3 is a group under composition.
(d) Let G4 be the set of all functions from R to R of the form f(x) =
ax3,where a is a nonzero real number. Prove or disprove: G4 is a group
under composition.
Transcribed Image Text:Proposition 8.8.3. Let A be a set, and let G be the set of all invertible functions from A to A. Then G is a group under composition. In the following exercise we look at some particular sets of functions, and investigate whether or not these sets form groups under composition. Recall that to show whether or not a set with binary operation is a group, you just need to show the properties: closure, identity, inverse, and associative. We're lucky in this case that we don't have to prove associative in every single case, because the operation of function composition is always associative, as we've proven before. So it's enough just to prove closure, identity, and inverse. Exercise 8.8.4. (a) Let G1 be the set of all nonzero functions from R to R of the form = ax, where a is a nonzero real number. (For example, the func- tions g(r) = -7x and h(x) = v2x are both elements of G1.) Prove or disprove: G1 is a group under composition. (Note: G1 is the set of nonzero linear functions from R to R.) (b) Let G2 be the set of all nonzero functions from R to R of the form f(x) zero. (For example, the functions p(x) = 29.4x + 42.3, q(x) = 15 and r(x) = -nx are all elements of G2.) Prove or disprove: G2 is a group under composition. (Note: G2 is called the set of all nonzero affine functions from R to R.) = ax + b where a and b are real numbers which are not both (c) Let G3 be the set of all nonconstant functions from R to R of the form f(r) = ax + b where a is a nonzero real number and b can be any real number. Prove or disprove: G3 is a group under composition. (d) Let G4 be the set of all functions from R to R of the form f(x) = ax3,where a is a nonzero real number. Prove or disprove: G4 is a group under composition.
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