how to find the value of sec theta -15/4 and Tan theta 12 when theta is greater than zero and less than 360

Answer 1

For all these, draw a triangle in the standard position. Then recall that

sinθ = y/r
cosθ = x/r
tanθ = y/x

For the first one here, you have

secθ = -15/4
so,
cosθ = -4/15
Now cosθ is negative in QII and QIII, so you find cos^-1(-4/15) in those quadrants.