MHB NEW Beginner's Trigonometry Identities Problem

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In this discussion, a beginner seeks help with finding sinΘ given that cosΘ = -4/9 in Quadrant II. It is clarified that the sine function is positive in Quadrant II, and the Pythagorean identity sin²Θ + cos²Θ = 1 is relevant for solving the problem. Participants emphasize the importance of visualizing the unit circle and suggest solving the identity for sin(Θ) to determine the correct root. Additionally, there are tips on using LaTeX for better presentation of mathematical functions. The conversation highlights the collaborative effort to understand trigonometric identities and their applications.
courtbits
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Alright. I am sort of understanding this section on my online math lesson, but I am still struggling with it. Would be gladly appreciated if someone could help me with this:

If cosΘ = -4/9 with Θ in Quadrant II, find sinΘ
 
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I want to ask you 2 questions:

  • What is the sign of the sine function in Quadrant II?
  • Is there an identity that can relate sine and cosine, that is, sine and cosine are the only two trig. functions present in the identity?
 
MarkFL said:
I want to ask you 2 questions:

  • What is the sign of the sine function in Quadrant II?
  • Is there an identity that can relate sine and cosine, that is, sine and cosine are the only two trig. functions present in the identity?

1) I have no idea what you are asking. v~v <== Dunce
2) Umm.. $${sin}^{2}\theta + {cos}^{2}\theta = 1$$ ...I think. o-o"

YAAS. I figured out how to use the Latex stuff. :D
 
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courtbits said:
1) I have no idea what you are asking. v~v <== Dunce
2) Umm.. $${sin}^{2}\theta + {cos}^{2}\theta = 1$$ ...I think. o-o"

YAAS. I figured out how to use the Latex stuff. :D

1.) Picture the unit circle, and a point on the circle in Quadrant II...is the $y$-coordinate positive or negative?

2.) Yes, good...since you are being asked to find the sine function, can you solve this identity for $\sin(\theta)$? And then the answer to part 1.) will tell you which root to take.

3.) Good job using $\LaTeX$. One suggestion...precede the trig. functions with a backslash, and they will not be italicized which makes them look like string of variables rather than pre-defined functions. For example, the code:

\sin^2(\theta)+\cos^2(\theta)=1

produces:

$\sin^2(\theta)+\cos^2(\theta)=1$

Also, for clarity, it is always a good idea to enclose the arguments of the functions in bracketing symbols...this way everyone knows exactly what the angle is. :D
 
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