First, we find the slope: \(\displaystyle{m}=\frac{{{y}{2}-{y}{1}}}{{{x}{2}-{x}{1}}}=\frac{{-{8}-{1}}}{{{5}-{2}}}=-\frac{{9}}{{3}}=-{3}\)

Use the slope-intercept form of a line and substitute the slope and a point, say (2,1) to find b: \(y=mx+b\)

\(1=-3(2)+b\)

\(1=-6+b\)

\(7=b\)

So, the equation of the linear function is \(y=-3x+7\)