$$(-2a^3b^2)^2 · 5a^2(b^2)^2 = 4a^6b^4 · 5a^2b^4 = 20a^8b^8$$
При $$a=2, b=\frac{1}{2}$$: $$20(2)^8(\frac{1}{2})^8 = 20(2 · \frac{1}{2})^8 = 20(1)^8 = 20$$