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4cosθ - 1 = 0 → cosθ = 1/4. For an acute angle, this gives θ ≈ 75.5°. Then tan(θ-15°) = tan(60.5°) ≈ 1.74. Using exact values may yield a different result. If cosθ = 1/4, then sinθ = √(1-1/16) = √15/4, tanθ = √15. Then tan(θ-15°) = (tanθ - tan15°)/(1+tanθ·tan15°). tan15° = 2-√3 ≈ 0.268, tanθ ≈ 3.873, giving approximately (3.873-0.268)/(1+3.873×0.268) = 3.605/2.038 = 1.769. 1/√3 ≈ 0.577, so not matching. There might be a misprint.