Q395
If a + 3b = 12 and ab = 9, then the value of (a - 3b) is:
A.
4
B.
7
C.
6
AnswerD.
9
Answer: Option C
Solution
Answer: Option C
Solution:
If a + 3b = 12ab = 9
(a - 3b)2 = a2 + 9b2 - 6ab
(a - 3b)2 = (a + 3b)2 - 12ab
(a - 3b)2 = 144 - 108
(a - 3b)2 = 36
(a - 3b) = 6