the Latex is not displaying so I will add a pic of my preview:
\(f(x)=\frac{sin(ax)}{bx}\qquad b\ne 0,\quad x\ne0\quad 4
Now at x=0.25 the gradient will be -4
so you need to differentiate this, then substitute in x=0.25
then solve for b given that f(0.25)=-4
Now you try it from there.
Coding:
f(x)=\frac{sin(ax)}{bx}\qquad b\ne 0,\quad x\ne0\quad 4 f(1)=0\\
f(1)=\frac{sin(a)}{b}=0\\
so,\\ sin(a)=0\\
a=n\pi\qquad n\in Z\\
\text{but}\quad 4 a=2\pi\\
f(x)=\frac{sin(2\pi x)}{bx}\qquad b\ne 0,\quad x\ne0\
