anonymous97
  • anonymous97
If sin Θ = 2 over 7 and tan Θ > 0, what is the value of cos Θ?
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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jamiebookeater
  • jamiebookeater
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anonymous
  • anonymous
so do you know SOHCAHTOA?
anonymous
  • anonymous
so if opposite over hypotenuse is 2/7 then cos is...
anonymous
  • anonymous
it is still 2/7

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More answers

anonymous
  • anonymous
because sin and cos of one angle is the same
welshfella
  • welshfella
one way to do it would be to use the identity cos^2 x = 1 - sin^2 x
anonymous
  • anonymous
|dw:1439852492795:dw|
anonymous
  • anonymous
|dw:1439852539120:dw|
welshfella
  • welshfella
No Sammy not always true
Nnesha
  • Nnesha
CAST rule for signs!!!
anonymous
  • anonymous
why not?
welshfella
  • welshfella
its only true for 45 degrees
anonymous
  • anonymous
i dont think so
anonymous
  • anonymous
oh i see
welshfella
  • welshfella
|dw:1439852609072:dw|
xapproachesinfinity
  • xapproachesinfinity
it will work why not just consider you working on first quadrant since tan>0 and sin>0 so must be first quad
welshfella
  • welshfella
another way would be to use pythagoras theorem to find the adjacent side then cos = adj / hyp
xapproachesinfinity
  • xapproachesinfinity
|dw:1439852745494:dw|
welshfella
  • welshfella
true
xapproachesinfinity
  • xapproachesinfinity
use Pythagoras to find x and then find cos theta
xapproachesinfinity
  • xapproachesinfinity
but the easiest way is the use of identity cos^2+sin^2=1 like @welshfella said
Nnesha
  • Nnesha
we can use that identity to find exact value of cos ?? aww never seen that before o.O
xapproachesinfinity
  • xapproachesinfinity
yeah why not?
xapproachesinfinity
  • xapproachesinfinity
you have sintheta =2/7 just put it into the equation and solve for cos
Nnesha
  • Nnesha
ohh got it i forgot to take square root
xapproachesinfinity
  • xapproachesinfinity
ah i see haha
xapproachesinfinity
  • xapproachesinfinity
square root produces two values you have to consider tan>0 again
anonymous97
  • anonymous97
A. 3 square root of 5 over 7 B. negative 3 square root of 5 over 7 C. 3 square root of 5 D. negative 3 square root of 5
anonymous97
  • anonymous97
those are my answer choices
welshfella
  • welshfella
cos^2 x = 1 - sin^2 x = 1 - 4/49 = 49/49 - 4/49 = 45/49 cos x = sqrt (45/49) can you finish this off?
welshfella
  • welshfella
hint factor 45 and look for perfect squares

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