If a and b are the roots of the equation x2 - 9x + 20 = 0, find the value of a2 + b2 + ab?  Choices.
A) -21	B) 1	C) 61	D) 21	E) None of these
a2 + b2 + ab = a2 + b2 + 2ab - ab   i.e., (a + b)2 - ab   from x2 - 9x + 20 = 0, we have   a + b = 9 and ab = 20. Hence the value of required expression (9)2 - 20 = 61.   ANSWER:61
<result>C</result>
If a and b are the roots of the equation x2 - 9x + 20 = 0, find the value of a2 + b2 + ab?