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If
tan (x) = (5)/(12)

and x is in third quarter
find :

sin(180+x) + tan(360-x) + (1)/(cos(180-x))
Please i want step by step not only the answer

User Dharmang
by
8.8k points

1 Answer

8 votes

Step-by-step explanation:

First, we need to find the values of the sine and cosine of x knowing the value of tan x and x being in the 3rd quadrant. Since tan x = 5/12, using Pythagorean theorem, we know that


\sin x = -(5)/(13)\;\;\text{and}\;\;\cos x = -(12)/(13)

Note that both sine and cosine are negative because x is in the 3rd quadrant.

Recall the addition identities listed below:


\sin(\alpha + \beta) = \sin\alpha\sin\beta + \cos\alpha\cos\beta


\Rightarrow \sin(180+x) = \sin180\sin x + \cos180\cos x


\;\;\;\;\;\;= -\sin x = (5)/(13)


\cos(\alpha - \beta) = \cos\alpha \cos\beta + \sin\alpha \sin\beta


\Rightarrow \cos(180 - x) = \cos180\cos x + \sin180\sin x


\;\;\;\;\;\;=-\cos x = (12)/(13)


\tan(\alpha - \beta) = (\tan\alpha - \tan\beta)/(1 + \tan\alpha\tan\beta)


\Rightarrow \tan(360 - x) = (\tan 360 - \tan x)/(1 + \tan 360 \tan x)


\;\;\;\;\;\;= -\tan x = -(5)/(12)

Therefore, the expression reduces to


\sin(180+x) + \tan(360-x) + (1)/(\cos(180-x))


\;\;\;\;\;= \left((5)/(13)\right) + \left((5)/(12)\right) + (1)/(\left((12)/(13)\right))


\;\;\;\;\;= (49)/(26)

User Maximus
by
7.5k points

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