$f_1(x) = \sin(x)$

$f_2(x) = \cos(x)$

$f_3(x) = e^x$

$f_4(x) = \frac{1}{x}$

f1(x) = sin(x)
f2(x) = cos(x)
f4(x) = 1 / x
f3(x) = ℯ^(x)
a = true
b = false
c = false
d = false
I1 = Integral(f1, 0, pi / 2)
I2 = Integral(f2, 0, pi / 2)
I4 = Integral(f4, 1, ℯ)
I3 = Integral(f3, 0, ln(2))