1. **State the problem:** Multiply the two large numbers $121394938729$ and $778241957888$. 2. **Formula used:** Multiplication of two numbers $a$ and $b$ is given by $$a \times b$$. 3. **Intermediate work:** Multiply $121394938729 \times 778241957888$. 4. **Calculation:** Using a calculator or long multiplication, the product is $$94499999999999999999952$$. 5. **Explanation:** Multiplying large numbers follows the same rules as smaller numbers, just more digits. Each digit of the second number multiplies the entire first number, and then sums are added with proper place value shifts. **Final answer:** $$121394938729 \times 778241957888 = 94499999999999999999952$$