We want to show that for any ϵ>0, there exists a δ>0 such that if 0<∣x−(−23)∣<δ, then ∣3+2x9−4x2−6∣<ϵ. First, let's simplify the expression inside the absolute value:
∣3+2x9−4x2−6∣=∣3+2x9−4x2−6(3+2x)∣=∣3+2x9−4x2−18−12x∣=∣3+2x−4x2−12x−9∣. We can factor the numerator:
−4x2−12x−9=−(4x2+12x+9)=−(2x+3)2. So, we have:
∣3+2x−(2x+3)2∣=∣2x+3−(2x+3)(2x+3)∣. As x→−23, 2x+3=0, so we can simplify further to: ∣−(2x+3)∣=∣2x+3∣=∣2(x+23)∣=2∣x+23∣=2∣x−(−23)∣. Now we want to find a δ>0 such that if 0<∣x−(−23)∣<δ, then 2∣x−(−23)∣<ϵ. So, 2∣x+23∣<ϵ. Dividing by 2, we get ∣x+23∣<2ϵ. Thus, we can choose δ=2ϵ. Let ϵ>0. Choose δ=2ϵ. If 0<∣x−(−23)∣<δ, then ∣3+2x9−4x2−6∣=2∣x+23∣=2∣x−(−23)∣<2δ=2(2ϵ)=ϵ.