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Question -

If sin x + cos x = 0 and x lies in the fourth quadrant, find sin x and cos x.



Answer -

Given:

Sin x + cos x = 0 and x lies in fourth quadrant.

Sin x┬а= -cos x

Sin x/cos x = -1

So, tan x = -1 (since, tan x = sin x/cos x)

We know that, in fourth quadrant, cos x and sec x arepositive and all other ratios are negative.

By using the formulas,

Sec x = тИЪ(1 + tan2┬аx)

Cos x = 1/sec x

Sin x = тАУ тИЪ(1- cos2┬аx)

Now,

Sec x = тИЪ(1 + tan2┬аx)

= тИЪ(1 + (-1)2)

= тИЪ2

Cos x = 1/sec x

= 1/тИЪ2

Sin x = тАУ тИЪ(1 тАУ cos2┬аx)

= тАУ тИЪ(1 тАУ (1/тИЪ2)2)

= тАУ тИЪ(1 тАУ (1/2))

= тАУ тИЪ((2-1)/2)

= тАУ тИЪ(1/2)

= -1/тИЪ2

тИ┤ sin x = -1/тИЪ2 and cos x= 1/тИЪ2

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