Question

For a sine function with amplitude =0.75 and period =10 , what is y(4) ?

Answer 1

Depends on the initial angle.

Answer 2

There's no phase shift mentioned, so I think we can assume it starts at x=0.

Answer 3

You need to develop a function of the form
\[\large y=Asin(Bx+C)\]
A=amplitude
B=frequency (for sine, it is 2π/T, T=period)
C=phase shift

Answer 4

The function sin x has amplitude 1 and period \[2\pi\]
Therefore your function can be expressed as \[0.75\sin \frac{ 2\pi }{ 10 }x\]
Just stick that with the right numbers into a calculator and you're sorted!