If \(s = 3i - j\) and \(t = 2i + 3j\), find \((t -
FURTHER MATHEMATICS
WAEC 2013
If \(s = 3i - j\) and \(t = 2i + 3j\), find \((t - 3s).(t + 3s)\).
- A. -77
- B. -71
- C. -53
- D. -41
Correct Answer: A. -77
Explanation
\(s = 3i - j; t = 2i + 3j\)
\( t - 3s = (2i + 3j) - 3(3i - j) = 2i + 3j - 9i + 3j = -7i + 6j\)
\(t + 3s = (2i + 3j) + 3(3i - j) = 2i + 3j + 9i - 3j = 11i\)
\((t - 3s).(t + 3s) = (-7i + 6j).(11i) = -77\)
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