SAT Math

Category - Algebra and Functions

What is the value of x2 + y2 − 8xy + x, if x = 0.9 and y = 0.1?
  1. 0
  2. 0.5
  3. 1
  4. 2
  5. 4
Explanation
Answer: C - The value of the expression is 1. Use x2 + 2xy + y2 = (x + y)2

x2 + y2 − 8xy + x = x2 + 2xy + y2 − 2xy − 8xy + x = (x + y)2 − 10xy + x = (0.9 + 0.1)2 − 10 × 0.9 × 0.1 + 0.9 = 12 − 0.9 + 0.9 = 1
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