sin(θ − ϕ); tan(θ) = 5/12 θ in Quadrant III, sin(ϕ) = − sqaure root10/10 ϕ in Quadrant IV.

Question

I used the sin equation
sin(a)cos(b)-sin(a)cos(b)

However I am still getting the wrong answer

Answer 1

in QIII
sinθ = -5/13
cosθ = -12/13

in QIV
sinϕ = -1/√10
cosϕ = 3/√10

sin(θ − ϕ) = (-5/13)(3/√10)-(-12/13)(3/√10) = 21/(13√10)

Answer 2

it was incorrect again :(

Answer 3

Better check my math, then. Also, maybe they don't want the radical in the denominator.