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Trigonometrical Equations
medium
ગણ $S=\left\{x \in R : 2 \cos \left(\frac{x^{2}+x}{6}\right)=4^{x}+4^{-x}\right\}$ ની સભ્ય સંખ્યા $.....$ થાય.
A
$1$
B
$3$
C
$0$
D
અનંત
(JEE MAIN-2022)
Solution
$2 \cos \left(\frac{x^{2}+x}{6}\right)=4^{x}+4^{-x}$
L.H.S $\leq 2 . \&$ R.H.S. $\geq 2$
Hence L.H.S $=2$ \& R.H.S $=2$
$2 \cos \left(\frac{x^{2}+x}{6}\right)=2 \quad 4^{x}+4^{-x}=2$
Check $x=0$ Possible hence only one solution.
Standard 11
Mathematics