## (click here to return)

If 5x - 1 = 19, then x = 4.

Proof:

5x - 1 = 19

if, and only if,

(5x - 1) + 1 = 19 + 1

if, and only if,

5x = 20

if, and only if,

(5x)/5 = 20/5

if, and only if,

x = 4

Therefore, 5x - 1 = 19 if, and only if, x = 4.

Therefore, if 5x - 1 = 19, then x = 4.

(end of page)

5x - 1 = 19

if, and only if,

(5x - 1) + 1 = 19 + 1

if, and only if,

5x = 20

if, and only if,

(5x)/5 = 20/5

if, and only if,

x = 4

Therefore, 5x - 1 = 19 if, and only if, x = 4.

Therefore, if 5x - 1 = 19, then x = 4.

(end of page)