anonymous
  • anonymous
i need an answer check!
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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anonymous
  • anonymous
the problem was \[\cos2\theta, when \sin \theta=-7/25 and \theta is \in Q3\] so cos2theta would be 527/625 right?
amistre64
  • amistre64
cos^2+sin^2 = 1 cos^2 = 1-sin^2 cos = sqrt(1-sin^2) ; and in q3 thats gonna be negative
anonymous
  • anonymous
but my teacher told us to use the double identity like cos 2A=1-2sin^2 ?

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amistre64
  • amistre64
i misread it then, it bites getting old :)
amistre64
  • amistre64
cos(a+a) = cosacosa-sinasina = cos^2(a) - sin^2(a) and thats where youd prolly use what i said at the start
amistre64
  • amistre64
cos^2 = 1-sin^2 cos^2-sin^2 = 1-sin^2 -sin^2 = 1-2sin^2
amistre64
  • amistre64
1- 98/25^2 = (25^2-98)/25^2
anonymous
  • anonymous
ok i see how u did it, that make a lot of sense thanks!
amistre64
  • amistre64
yw

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