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If \(\sin x = \frac{4}{5}\), find \(\frac{1 + \cot^2 x}{\csc^2 x - 1}\).

Mathematics
JAMB 2019

If \(\sin x = \frac{4}{5}\), find \(\frac{1 + \cot^2 x}{\csc^2 x - 1}\).

  • A. \(\frac{13}{2}\)
  • B. \(\frac{25}{9}\)
  • C. \(\frac{3}{13}\)
  • D. \(\frac{4}{11}\)
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Correct Answer: Option B
Explanation

\(\sin x = \frac{opp}{Hyp} = \frac{4}{5}\)

5\(^2\) = 4\(^2\) + adj\(^2\)

adj\(^2\) = 25 - 16 = 9

adj = \(\sqrt{9}\) = 3

\(\tan x = \frac{4}{3}\)

\(\cot x = \frac{1}{\frac{4}{3}} = \frac{3}{4}\)

\(\cot^2 x = (\frac{3}{4})^2 = \frac{9}{16}\)

\(\csc x = \frac{1}{\sin x}\)

= \(\frac{1}{\frac{4}{5}} = \frac{5}{4}\)

\(\csc^2 x = (\frac{5}{4})^2 = \frac{25}{16}\)

\(\therefore \frac{1 + \cot^2 x}{\csc^2 x - 1} = \frac{1 + \frac{9}{16}}{\frac{25}{16} - 1}\)

= \(\frac{25}{16} \div \frac{9}{16}\)

= \(\frac{25}{9}\)

There is an explanation video available below.


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Explanation Video

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WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC offline past questions - with all answers and explanations in one app - Download for free