Question

Which of these is a correct identity? x + 4x = 5x 6x = 18 2x + 1 = 7 7x + 9 = x

Answer 1

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.