91 does not end in 0 or 5, so it is not divisible by 5.
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- To find the smallest prime factor of 91, test divisibility by the smallest prime numbers.
- 91 is odd, so it is not divisible by 2.
- Sum of digits of 91 is \(9 + 1 = 10\), which is not divisible by 3, so 91 is not divisible by 3.
- Check divisibility by 7:
- \[ 91 \div 7 = 13 \]
- 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 $.
