I can do your 2nd problem but not the 1st, for you've
made a mistake in copying the first problem. Here's why:
sinq = 12/13, 3p/2 < q < 2p. Find sin2q, cos2q, tan2q?
3p/2 < q < 2p
tells us that q is in quadrant IV.
But the sine is negative in quadrant IV, yet you have
sinq = 12/13, which is a positive number.
That cannot be.
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Here's your 2nd problem:
cosq = -1/4,cscq > 0, find sin2q,cos2q, tan2q
This tells us that q is in quadrant II,
because that is the only quadrant in which the cosine is negative and
the cosecant is positive.
So we draw an angle in Quadrant II to represent angle q
Next we draw a perpendicular to the x axis. Since the cosine
is , we make the x value -1, which is the numerator of
and make the hypotenuse or the r equal to the the
denominator of which is 4:
Next we calculate the value of y by the Pythagorean
theorem equation
So we label the y-value with that
Now we can find sin2q using the
identity:
sin2q = 2sinqcosq
because we now know that sinq = = , and cosq = = .
sin2q = 2sinqcosq =
Next we find cos2q using any one of
these three identities:
cos2q = cos2q - sin2q
cos2q = 2cos2q - 1
cos2q = 1 - 2sin2q.
I'll choose the second one, although any one will give you the
same answer:
cos2q = 2cos2q - 1
cos2q = 2 - 1
cos2q = 2 - 1
cos2q = - 1
cos2q = - 1
cos2q =
Finally we can find tan2q from
the identity
tan2q = sin2q/cos2q
tan2q =
Edwin