Advanced Math practice question

Answer: 3

Expand: (4x² − 20x + 25) − (4x² + 20x + 25) = −40x. So −40x = −120 and x = 3. (Shortcut: a² − b² = (a − b)(a + b) with a = 2x − 5 and b = 2x + 5 gives (−10)(4x) = −40x.)

Common wrong answers

If you answered 6

6 comes from −20x = −120, subtracting only one of the two 20x terms.

If you answered -3

−3 has the wrong sign: −40x = −120 gives x = 3.

If you answered 2.4

2.4 comes from −50x = −120, wrongly keeping the constants in the difference.

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