已知tanθ=3,求4sin²θ-3sinθcosθ-5cos²θ=?
4sin²θ-3sinθcosθ-5cos²θ=(4sin²θ-3sinθcosθ-5cos²θ)/(sin²θ+cos²θ)(分子分母同除以cos²θ)
=(4tan²θ-3tanθ-5)/(tan²θ+1)=(36-9-5)/(9+1)=22/10=11/5