A function f is onto if and only if, each element in the codomain of f is the image of at one element in the domain of f

A function f is onto if and only if, each element in the codomain of f is the image of at least one element in the domain of f.

Step-by-step explanation:

A function f is onto if and only if, each element in the codomain of f is the image of at least one element in the domain of f.

Let us consider a function f which maps the elements of X to each element in the domain of f, such that

f(1) = D

f(2) = B

f(3) = C

f(4) = C

From here, we can determine the domain and range, so

Domain  X of f = {1, 2, 3, 4}

Domain  Y of f =  {D, B, C}

Therefore, it is clear that every element in the codomain of f is the image of at least one element in the domain of f.

to find the perimeter of the rectangle this is the expression:

x-9+x-9+3x-4+3x-4=138

if we simplify it:

8x-26=138

remember, 138 is what it all adds up to

the length is 11.5cm

the width is 57.5cm

the area is 661.25cm^2

the answers might not be correct use at own risk