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Advanced Math / Nonlinear equations in one variable and systems of equations in two variables Difficulty: Medium

If 4x-4=112, what is the positive value of x - 1 ?

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Explanation

The correct answer is 28 . The given absolute value equation can be rewritten as two linear equations: 4 x - 4 = 112 and -4x-4=112, or 4 x - 4 = -112 . Adding 4 to both sides of the equation 4 x - 4 = 112 results in 4 x = 116 . Dividing both sides of this equation by 4 results in x = 29 . Adding 4 to both sides of the equation 4 x - 4 = -112 results in 4 x = -108 . Dividing both sides of this equation by 4 results in x = -27 . Therefore, the two values of x - 1 are 29-1, or 28 , and -27-1, or -28 . Thus, the positive value of x - 1 is 28 .

Alternate approach: The given equation can be rewritten as 4x-1=112, which is equivalent to 4x-1=112. Dividing both sides of this equation by 4 yields x-1=28. This equation can be rewritten as two linear equations: x - 1 = 28  and -x-1=28, or x - 1 = -28 . Therefore, the positive value of x - 1 is 28 .