Multiple Choice Question (MCQ)
If a+2b = 10, 2ab = 9, then a2b =

×
2

×
4

×
6

✓
8
If a+2b = 10, 2ab = 9, then a2b =
2
4
6
8
Given condition
Square both sides of the equation
(a+2b)^2 = 100
Expand the LHS
a^2+4b^2+2\cdot 2ab = 100
then,
a^2+4b^2 = 1002\cdot 2ab = 1002\cdot 9 = 82
that is
On the other hand, construct an equation using the conjugate of a+2b
Substituting (1) and (2) results in
(a2b)^2 = 2\cdot 82100=64
Therefore
a2b = 8
D is the correct option