Question

(R + RCos (2,57 (20)) = 12), How to solve for R?

Answer 1

This solution is based on `cos(2.57xx20)`
`R~~7.390` to 3 decimal places
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`R=12/(1+cos(2.5720)) ~~6.003` to 3 decimal places

Explanation:

Given: `R+Rcos(2.57(20))=12`

Factor out the R giving

`R(1+cos(2.57(20))=12`

Divide both sides by `(1+cos(2.57(20))` giving

`R xx (1+cos(2.57(20)))/(1+cos(2.57(20))) =12/(1+cos(2.57(20)))`

But `(1+cos(2.57(20))) /(1+cos(2.57(20))) =1` giving

`R=12/(1+cos(2.57(20)))`

`R~~7.390` to 3 decimal places

This solution is based on `cos(2.57xx20)`

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Or, if you meant:
`R=12/(1+cos(2.5720))`

`R=6.003` to 3 decimal places