1.
Let f(x)={ax+1,x<13,x=1bx2+1,x>1f(x) = \begin{cases} ax + 1, & x < 1 \\ 3, & x = 1 \\ bx^2 + 1, & x > 1 \end{cases}. If f(x)f(x) is continuous at x=1x = 1, then (ab)(a - b) is equal to: