SAT官方数学习题 9月6日

Correct Answer: D

• Here's Why:

   

  Roman Numeral Answer Format

  Roman Numeral I: Can the value of x be –?

  You could test this answer by substituting – for x in the equation and seeing whether the result is true. But you can also reason this question out without substituting numbers:

  If x = – , then is a positive number, because any nonzero number squared is positive.

  If x = –, then is negative.

  So is negative and x² is positive.

  Therefore, x cannot be –.

  Mark Roman numeral I with an “F” for false.

  Roman Numeral II: Can the value of x be 0?

  This is a very easy substitution to make:

  = x²

  = 0² = 0

  Roman numeral II is true, so mark it with a “T” for true.

  Roman Numeral III: Can the value of x be ?

  Substitute for x:

  If x = , then = .

  Also, x² = = .

  Roman numeral III is true, so mark it with a “T” for true.

  Check the Answers:

  You now know whether each of the Roman numeral statements is true or false:

  I is false.
  II is true.
  III is true.

  Find the choice that says only II and III are true.

• Difficulty: Hard
• Question Type: Standard Multiple Choice