- #1
matrixone
- 28
- 2
The number of real roots of the equation
$$2cos \left( \frac {x^2 + x} {6} \right)=2^x + 2^{-x}$$
Answer options are : 0,1,2,∞
My approach :
range of cos function is [-1,1]
thus the RHS of the equation belongs to [-2,2]
So, we have
-2 ≤ 2x + 2-x ≤ 2
solving the right inequality, i got 2x = 1 and that satisfies the left part too
therefore , x can take only one value = 0
Now since this values agrees with the orginal trigonometric equation, we have 1 real root for this equation
So answer is 1
Is my approach/answer correct ?
$$2cos \left( \frac {x^2 + x} {6} \right)=2^x + 2^{-x}$$
Answer options are : 0,1,2,∞
My approach :
range of cos function is [-1,1]
thus the RHS of the equation belongs to [-2,2]
So, we have
-2 ≤ 2x + 2-x ≤ 2
solving the right inequality, i got 2x = 1 and that satisfies the left part too
therefore , x can take only one value = 0
Now since this values agrees with the orginal trigonometric equation, we have 1 real root for this equation
So answer is 1
Is my approach/answer correct ?