sin^2 73°(1+tg^2 17°)-2tg15° * 75°

Using trigonometric identities:
sin^2(90°-17°)(1+(sin^2 17°/cos^2 17°))-2(tan 15° * tan 75°)

Since sin(90°-θ) = cosθ:
cos^2 17°(1+(sin^2 17°/cos^2 17°))-2(tan 15° * tan 75°)

Using the Pythagorean identity sin^2θ + cos^2θ = 1:
cos^2 17°(1+(1-cos^2 17°/cos^2 17°))-2(tan 15° * tan 75°)

Simplifying:
cos^2 17°(1+1-1)-2(tan 15° tan 75°)
cos^2 17°-2(tan 15° tan 75°)

Using the tangent addition formula tan(A+B) = (tanA + tanB) / (1 - tanAtanB):
cos^2 17°-2((tan 15° + tan 75°) / (1 - tan 15° tan 75°))

Since tan 15° = tan(45°-30°) = (tan 45° - tan 30°) / (1 + tan 45° tan 30°):
cos^2 17°-2(((1 - sqrt(3)/3) + sqrt(3)) / (1 + sqrt(3)/3 sqrt(3)))

Now, it can be simplified further, but this is the general process to follow to simplify the given expression.