wrong answer (Question:556440.0)

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priyankameena 21219

· started a discussion

· 1 Months ago

wrong answer (Question:556440.0)

cosx-cosy=-2[sin(x+y)\2][sin(x-y)\2] which implies that answer must be -1

Question:

What is the value of [(sin x + sin y) (sin x – sin y)]/[(cosx + cosy) (cosy – cosx)]?

Options:

– 1

Solution:

$\begin{matrix} \frac{(s i n x + s i n y) (s i n x - s i n y)}{(c o s x + c o s y) (c o s y - c o s x)} = \frac{[2 s i n (\frac{x + y}{2}) c o s (\frac{x - y}{2})] [2 c o s (\frac{x + y}{2}) s i n (\frac{x - y}{2})]}{[2 c o s (\frac{x + y}{2}) c o s (\frac{x - y}{2})] [2 s i n (\frac{x + y}{2}) s i n (\frac{x - y}{2})]} \\ = 1 \end{matrix}$

Alternative method:-

$= > \frac{(s i n 0 ° + s i n 90 °) (s i n 0 ° - s i n 90 °)}{(c o s 0 ° + c o s 90 °) (c o s 0 ° - c o s 90 °)} = \frac{1 \times (- 1)}{1 \times (- 1)} = 1$

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