Given sinθ=35impliesopp=3,hyp=5
Using Pythagoras' Theorem, we have adj=√52−32=√16=4
∴\cosθ=45,0°<θ<90°
In the quadrant where 180°−θ lies is the 2nd quadrant and here, only sinθ=+ve.
∴\cos(180−θ)=−ve=−45