NEET Class neet Answered
If tantita- ?5\2 then value of cos tita is
![question image](http://images.topperlearning.com/topper/new-ate/top_mob16565188194691186674f774762-149a-4661-b6c0-ea5e076f0f74.jpg)
Asked by razaqasmi87 | 29 Jun, 2022, 21:36: PM
![begin mathsize 14px style tan theta space equals space fraction numerator sin theta over denominator cos theta end fraction space equals fraction numerator square root of 1 minus cos squared theta end root over denominator cos theta end fraction space equals fraction numerator square root of 5 over denominator 2 end fraction end style](https://images.topperlearning.com/topper/tinymce/cache/05f728e7cf97f5ac48d4ceba00f8a44f.png)
By squaring both sides of last two expressions in above mathematical statement,
we get
![begin mathsize 14px style fraction numerator 1 minus cos squared theta over denominator cos squared theta end fraction space equals 5 over 4 end style](https://images.topperlearning.com/topper/tinymce/cache/79cbe7c08611ee956cae194848ec93a3.png)
let x = cosθ , then we have ![begin mathsize 14px style fraction numerator 1 minus x squared over denominator x squared end fraction space equals space 5 over 4 end style](https://images.topperlearning.com/topper/tinymce/cache/7ef9c080db918d49897c32ee2ef6ebbe.png)
![begin mathsize 14px style fraction numerator 1 minus x squared over denominator x squared end fraction space equals space 5 over 4 end style](https://images.topperlearning.com/topper/tinymce/cache/7ef9c080db918d49897c32ee2ef6ebbe.png)
By solving above equation, we get x = cosθ = 2/3
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Alternate method
![](https://images.topperlearning.com/topper/tinymce/imagemanager/files/7e00060d1e81f6bcf6285b578ab5d84962bc9f325ba9f3.93552319f1.png)
Let us consider a triangle ABC such that
A = 90o ,
B = θ ,
![begin mathsize 14px style angle end style](https://images.topperlearning.com/topper/tinymce/cache/f1d45fc0daa19a85e39a8446cd27e48f.png)
![begin mathsize 14px style angle end style](https://images.topperlearning.com/topper/tinymce/cache/f1d45fc0daa19a85e39a8446cd27e48f.png)
side AC = √5 units and AB = 2 units , so that tanθ = √5 / 2
Side BC can be calculated as 3 unitsas given below
![begin mathsize 14px style B C space equals space square root of A C squared plus A B squared end root space equals square root of 5 plus 4 end root space equals space 3 space u n i t s end style](https://images.topperlearning.com/topper/tinymce/cache/ca6ff1920435cab2250a875e31e8789e.png)
Then cosθ = 2/3
Answered by Thiyagarajan K | 30 Jun, 2022, 00:26: AM
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