Explanation

Note: the stem prints '7/2', but sinθ+cosθ ≤ √2, so a square-root was lost in transcription — read √7/2. Then (sinθ−cosθ)² = 2−(sinθ+cosθ)² = 2−7/4 = 1/4, giving sinθ−cosθ = 1/2. That is option B (its text 'rac12' is a garbled rendering of 1/2).