знайти похідну f(x)=sin^4 x+cos^4 x
f"(PI/4)-?

f'(x) = 4cos4x-4sin4xf''(x) = -16sin4x-16cos4xf''(pi/4) = -16sin(4*pi/4)-16cos(4*pi/4)f''(pi/4) = -16sin(pi)-16cos(pi) = 0-(-1)=1