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If a^3bc^2 < 0, which of the following must be correct? [Without calculator]\newline(A) a < 0 \& c < 0\newline(B) b < 0 \& c < 0\newline(C) a < 0 \& b > 0\newline(D) a < 0 \& b > 0 or a > 0 \& b < 0

Full solution

Q. If a3bc2<0a^3bc^2 < 0, which of the following must be correct? [Without calculator]\newline(A) a<0&c<0a < 0 \& c < 0\newline(B) b<0&c<0b < 0 \& c < 0\newline(C) a<0&b>0a < 0 \& b > 0\newline(D) a<0&b>0a < 0 \& b > 0 or a>0&b<0a > 0 \& b < 0
  1. Analyze Given Options: We know that a^3 \cdot b \cdot c^2 < 0. Since a3a^3 and c2c^2 are both raised to an even power, they will always be non-negative (zero or positive) regardless of the sign of aa and cc. Therefore, the sign of the expression is determined by the sign of bb and the sign of aa (since a negative number raised to an odd power is negative). If bb is positive, then aa must be negative for the expression to be negative. If bb is negative, then aa can be either positive or negative.
  2. Option (A): Let's analyze the options given:\newline(A) a < 0 & c < 0: This is not necessarily true because cc could be positive and the expression could still be negative as long as aa is negative and bb is positive.
  3. Option (B): (B) b < 0 & c < 0: This is not necessarily true because cc could be positive and the expression could still be negative as long as aa is negative and bb is positive.
  4. Option (C): CC a < 0 & b > 0: This could be true because if aa is negative and raised to an odd power, it remains negative, and if bb is positive, the expression would be negative. However, this does not cover all cases because bb could also be negative.
  5. Option (D): (D) a < 0 \& b > 0 or a > 0 \& b < 0: This must be correct because it covers all cases where the expression could be negative. If aa is negative and bb is positive, the expression is negative. If aa is positive and bb is negative, the expression is also negative. This option accounts for the fact that the sign of a3a^3 is determined by the sign of aa, and the overall sign of the expression is determined by the sign of bb.

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