Algebramedium · Past Paper
What must be added to x^2 + 6x to make it a perfect square?
A3
B6
C9
D36
✓ Correct Answer: C — 9
A perfect square is (x+a)^2 = x^2 + 2ax + a^2. Here 2a=6, so a=3 and a^2=9.
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