The simple trick of the square of 45

$$(50 - 5)^2 = 50^2 - 2 \times 50 \times 5 + 5^2$$ $$= 2500 - 500 + 25$$ $$= 2000 + 25 = 2025$$

Subtract the deviation from 50 to get the first digits: $50 - 5 = 45$.
Square the deviation for the last two digits: $5^2 = 25$.
Combine: $45\, 25$.

Final answer: $\mathbf{45^2 = 2025}$

2025