We have,
f(x)={\begin{matrix}\mathrm{sin}x-{e}^{x} & \mathrm{if}x\leq 0 \\ a+[-x] & \mathrm{if}0<x<1 \\ 2x-b & \mathrm{if}x\geq 1\end{matrix}
If f(x) is continuous at x=a then x→a−limf(x)=f(a)=x→a+limf(x).
Continuous at x=0
f(0+)=f(0−)
⇒a−1=0−e0
⇒a=0
Continuous at x=1
f(1+)=f(1−)
⇒2(1)−b=a+(−1)
⇒b=2−a+1
⇒b=3
∴a+b=3