Answer:
It's the first choice.
Step-by-step explanation:
cos θ = √(1 - sin^2 θ ) and cos θ will be positive because sin θ > 0 tan θ > 0. The angle θ will be in the first quadrant.
cos θ = √( 1 - (2/7)^2)
cos θ = √(1 - 4/49) = √(45/49)
cos θ = √9√5 / 7
cos θ = 3√5 / 7.
