The number of solutions of the equation 2 2 + 5 2 = 2 3 5 2 in [- 2, 2 ] is :
- 5
- 7
- 6
- 9
Answer
(2) 7
Solution
Using 4 3 A = 3A + 3 A with A = 5 2,
2 3 5 2 = 12 ( 15 2 + 3 5 2 )
so the equation becomes
2 2 2 + 2 5 2 = 15 2 + 3 5 2
2 2 2 = 15 2 + 5 2
2 2 2 = 5 2 + 3 2,
3 2 = 15 2
15 2 = 2n 3 2, n Z
6 = 2n or 9 = 2n
= n 3 or = 2n 9
In [- 2, 2 ], = n 3 gives 0, 3 and = 2n 9 gives 0, 2 9, 4 9.
The distinct solutions are 0, 3, 2 9, 4 9, i.e. 7 solutions.
Answer: (2)