Find the angle between i + 5j and 5i - J
FURTHER MATHEMATICS
WAEC 2020
Find the angle between i + 5j and 5i - J
- A. 0°
- B. 45°
- C. 60°
- D. 90°
Correct Answer: D. 90°
Explanation
a = i + 5j and b = 5i - j
cos\(\theta\) = \(\frac{a.b}{|a|.|b|}\)
= \(\frac{(1 \times 5) + (5x - 1)}{(\sqrt{1^2 + 5^2}) (5^2 + (-1))^2}\)
= \(\frac{5 - 5}{\sqrt{26}\times \sqrt{26}}\) = 0
x = cos\(^{-1}\)(0), x = 90\(^o\)
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