Half Angle Formula Positive or Negative?

When using the half angle formula for sine and cosine learn whether the result is positive or negative. We go through an example in this free math video tutorial by Mario's Math Tutoring.

0:27 Example 1 Finding the sin(5pi/8) using half angle formula
1:14 How to tell whether the sine half angle is positive or negative

Other Helpful Related Videos:

More Half Angle Examples:

Double Angle Examples:

Sum and Difference Formulas:

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[minkim]

you just cleared up so much for me in less than two minutes when the book couldn't do so. Thank you for your quick and straight-to-the-point explanations. Thank you very much

[sharvinjoshi]

What is the problem doesnt give you a value present on the unit circle?

[samgardner]

Thanks for all of your help Mr.Mario!! I got stuck with a mediocre professor and an even worse lecturer in an online class, your videos really help clarify the topics we're covering.

[agelectronics]

Hi, how would you find if it is positive or negative if what you are given is not in pi or degrees and it is just numbers

[emilyyoo]

as school starts i'm legit going to your channel everyday for precalc help

[nighthunterian]

What if you don't have pi? just a cosine value like -9/16

[mealomemes]

This was a really easy to understand explanation and made this much less difficult for me, thank you !

[alisonm]

Can you post a video with numbers only like for example csc x = 3 in QII. Because I’m having trouble with cos x/2 with the negative outside. I don’t get why it’s negative

[sccm]

What if you just transform to degrees? Doesn't that directly tell you it's 112 degrees which is QII and positive?

[garrettludescher]

FUCKING LIFE SAVER. Excuse my language but omg I have never understood why(or just made stuff up) until now. Thank you! I have my trig final tomorow

[vedradhakrishnan]

Studying for midterms and watched this because I forgot.

[pizzaboy]

Thank you so much I wish I could kiss you