Rate of change using trig functions.

An equation of the tangent line to the curve https://nernst.chem.sfu.ca/cgi-bin/m...0%5Csin%20x%29

at the point https://nernst.chem.sfu.ca/cgi-bin/m...283%20%5Cpi%29 is *y* =

(point intercept form: y = mx+b)

I know it's easier to fine f(3π) ans f'(3π) and then simplifty the exact value of sin(3π) and cos(3π)...

So I got

f(3π) = 3π((5cos(3π)-9sin(3π))) = -15π

f'(3π) = 3π(-5sin(3π)-9cos(3π))+5cos(3π)-9sin(3π) = -26.99

but I dont know what to do with these values and or if i've gone to correct way of solving this. any help would be wonderful!