For sin−1(x2−2x−21) to be defined, we need x2−2x−21≤1, i.e., ∣x2−2x−2∣≥1.
Case 1:
x2−2x−2≥1⇒x2−2x−3≥0
⇒(x−3)(x+1)≥0
⇒x≤−1 or x≥3.
Case 2:
x2−2x−2≤−1⇒x2−2x−1≤0
⇒(x−1)2≤2
⇒1−2≤x≤1+2.
Domain =(−∞,−1]∪[1−2,1+2]∪[3,∞).
So α=−1, β=1−2, γ=1+2, δ=3.
α+β+γ+δ=−1+1−2+1+2+3=4.