An obvious substitution would be x=sin(t), √(1x^2) = cos(t), so we have
f(sin(t))+f(cos(t)) = 2
which looks a bit nicer. We do not know if f is differentiable, but if we assume it is, when we differentiate both sides, we get
f'(sin(t)) / f'(cos(t)) = sin(t) / cos(t)
to which f'(x) = x is an obvious solution. Hence f(x) = x^2/2 + C. When we plug this into the original equation and solve for C, we get
f(x) = x^2/2 + 3/4
Insert this into the wanted integrand and we get  quite obviously ;)  the result
π/2

Posted by JLo
on 20191214 05:34:55 