1.

t = [0:1/8000:8191/8000];
x = sin(2*pi*100*t + 2*pi*100*(t.*t));

p = length(x);
f = fft(x)/p;
magnitude(1) = abs(f(1));
upper = p/2;
magnitude(2:upper) = 2*abs(f(2:upper));
magnitude(upper+1) = abs(f(upper+1));

plot(magnitude, t)