Since 13 is a whole number, 91 is divisible by 7. Therefore, the smallest prime factor of 91 is \(\boxed{7}\).Question: If $ a + b = 7 $ and $ a^2 + b^2 = 25 $, find the value of $ ab $.

["Finding $ ab $ Given $ a + b = 7 $ and $ a^2 + b^2 = 25 $", "Understanding the relationship between the sum, sum of squares, and product of two numbers is essential in algebra. Given the equations:", "- $ a + b = 7 $\n- $ a^2 + b^2 = 25 $", "We can use a key identity from algebra to find $ ab $ efficiently.", "### Step 1: Use the identity for the square of a sum\nRecall the formula:\n[\n(a + b)^2 = a^2 + 2ab + b^2\n]", "Substitute the known values:\n[\n7^2 = 25 + 2ab\n]", "[\n49 = 25 + 2ab\n]", "### Step 2: Solve for $ ab $\nSubtract 25 from both sides:\n[\n24 = 2ab\n]", "Divide both sides by 2:\n[\nab = 12\n]", "### Conclusion\nThus, the value of $ ab $ is (\boxed{12}).\nThis technique efficiently connects sums and sums of squares to find products, especially useful when working with prime factorization or integer solutions like the earlier problem involving divisibility and whole numbers."]