WAEC - Further Mathematics (2024 - No. 30)
In triangle XYZ, |XY| = 10cm, |YZ| = 9 cm and |XZ| = 7 cm. If XZY = \(\alpha\), find the value of cos \(\alpha\).
\(\frac{11}{15}\)
\(\frac{17}{35}\)
\(\frac{5}{21}\)
\(\frac{7}{32}\)
Explanation
Using, cos \(\alpha\) = \(\frac{ b^2 + c^2 - a^2}{2bc}\)
cos \(\alpha\) = \(\frac{ 9^2 + 7^2 - (10)^2}{2 \times 9 \times 7}\)
= \(\frac{ 130 - 100}{126}\) = \(\frac{30}{126}\) = \(\frac{5}{21}\)
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