Trigonometry Functions and Angles

1)If sin(t) = -5/13 and 270 degrees is less than or
equal to t and is less than or equal to 360 degrees,
then cos(t)=?

2)If 0 degrees is less than t and less than 90 degrees
and cos(t) = 4/5, then cos(2t)=?

3)A right triangle is shown, sec(t) =? . |
1 = hypotenuse . |
x = y side of triangle . | x
t = inside angle < t___________|

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...is positive so the answer is 12/13.
2)cos(2t)=2*cos(t)^2-1=2*(16/25)-1=32/25-1=7/25 (and it does not matter here where t is).
3)sec(t)=1/cos(t) ...