Answer:
x + 4x = 5x
Step-by-step explanation:
An identity is a mathematical equation that is always true (here - for all possible x's).
a). x + 4x = 5x; this is true, because for any possible x
x+4x = (1 + 4)x = 5x; there's not much to add.
b). 6x=18; evaluates to
x = 3; so it only works for one x, not all possible xs.
c). 2x + 1 = 7
2x = 6
x = 3; so it only forks for one x
d). 7x + 9 = x
6x + 9 = 0; we could compute the exact x it works for from here, but suffice to say this doesn't work for x = 0.
In between these given equations, x + 4x = 5x is the correct identity here.
"An identity is an equality relating one mathematical expression A to another mathematical expression B, such that A and B produce the same value for all values of the variables within a certain range of validity."
Given equations are:
1. x + 4x = 5x
⇒ 5x = 5x
This equation is true for all values of 'x'.
Hence, this is a correct identity.
2. 6x = 18
⇒ x = 3
This equation is true when x = 3.
3. 2x + 1 = 7
⇒ 2x = 6
⇒ x = 3
This equation is true when x = 3.
4. 7x + 9 = x
⇒ 6x = - 9
⇒ x = - 9/6
⇒ x = - 3/2
This equation is true when x = - 3/2.
Learn more about an identity here: https://brainly.com/question/12984949
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