If a - b = 4 and a2 + b2 = 18, find the value of ab.
Pick: A) 9 B) 1 C) 2 D) 18 E) 19
2ab = (a2 + b2) - (a - b)2   = 18 - 16= 
<gadget id="calculator">18 - 16</gadget>
<output>2</output>
2   ab= 1.   Answer: 1
<result>B</result>
If a - b = 4 and a2 + b2 = 18, find the value of ab.