Equation of line $: y=m x+c$
Since the line goes through $(0,1)$, Hence $1=m\ast 0+c$
So, $c=1$.
Line goes through $(-1,0)$ : So, $0=-1 \ast m+1 \Rightarrow m=1$
Line equation $: y=x+1$
Integral of $(1+x)$ is $(1+x)^2 / 2$
So, from $x=1$ to $2 ,$ it becomes $9 / 2-4 / 2=5 / 2=2.5.$
