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How can I solve the following trigonometry problem?
It says that the value of sina is 1/3, and based on that I have to find out the value of cos2a.
I thought of using the cos2a formula, but that didn't do me much good.
Any help, please?
2 Answers
- Marley KLv 71 decade agoFavorite Answer
draw a right triangle.
label one of the acute angles a.
label the opposite side 1 and the hypotenuse 3 (sina=1/3)
use the pythagorean theorem to find the 3rd side: 2√2
now you know cosa = 2√2 /3
use the cos2a formula: cos2a = cos²a - sin²a:
(2√2/3)² - (1/3)²
= 8/9 - 1/9
= 7/9
actually, another cos2a formula is: 1 - 2sin²a
which is easier because then you have:
cos2a = 1 - 2(1/3)²
= 1 - 2(1/9)
= 1 - 2/9
= 7/9
that's it! ;)
- Anonymous5 years ago
What Grade? in the journey that your in highschool, use your scientific calc.....it's going to provide you the respond....additionally in the journey that your textbooks are like mine....it's going to have the solutions in the lower back.... i could do the difficulty in spite of the undeniable fact that it dosent appear like something i comprehend....evidently VERY unframilliar?
