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If \(\sin x° = \frac{a}{b}\), what is \(\sin (90 - x)°\)?

Mathematics
JAMB 1981

If \(\sin x° = \frac{a}{b}\), what is \(\sin (90 - x)°\)?

  • A. \(\frac{\sqrt{b^2 - a^2}}{b}\)
  • B. 1\(\frac{-a}{b}\)
  • C. \(\frac{b^2 - a^2}{b}\)
  • D. \(\frac{a^2 - b^2}{b}\)
  • E. \(\sqrt{b^2 - a^3}\)
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Correct Answer: Option A
Explanation

\(\sin x = \frac{a}{b}\)

\(\sin^{2} x + \cos^{2} x = 1\)

\(\sin^{2} x = \frac{a^{2}}{b^{2}}\)

\(\cos^{2} x = 1 - \frac{a^{2}}{b^{2}} = \frac{b^{2} - a^{2}}{b^{2}}\)

\(\therefore \cos x = \frac{\sqrt{b^{2} - a^{2}}}{b}\)

\(\sin (90 - x) = \sin 90 \cos x - \cos 90 \sin x\)

= \((1 \times \frac{\sqrt{b^{2} - a^{2}}}{b}) - (0 \times \frac{a}{b})\)

= \(\frac{\sqrt{b^{2} - a^{2}}}{b}\)


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JAMB CBT Software 2025 - Free Download
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
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WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
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