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If x + y = 90 simplify \((sinx + siny)^2\)−2sinxsiny

Mathematics
JAMB 2015

If x + y = 90 simplify \((sinx + siny)^2\)−2sinxsiny

  • A. 1
  • B. 0
  • C. 2
  • D. -1
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Correct Answer: Option A
Explanation

Given: \(x + y = 90° ... (1)\)

\((\sin x + \sin y)^{2} - 2\sin x \sin y = \sin^{2} x + \sin^{2} y + 2\sin x \sin y - 2\sin x \sin y\)

= \(\sin^{2} x + \sin^{2} y ... (2)\)

Recall: \(\sin x = \cos (90 - x) ... (a)\)

From (1), \(y = 90 - x ... (b)\)

Putting (a) and (b) in (2), we have

\(\sin^{2} x + \sin^{2} y \equiv \cos^{2} (90 - x) + \sin^{2} (90 - x)\)

= 1

There is an explanation video available below.


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Explanation Video

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