A) 3
B) 4
C) 5
D) 2
Correct Answer: B
Solution :
Let \[\cos \,\,x=t,\] so that given equation reduces to \[5t+\frac{5}{2t}-5=2{{t}^{2}}+\frac{1}{2{{t}^{2}}}\] \[\Rightarrow \] \[4{{t}^{4}}-10{{t}^{3}}+10{{t}^{2}}-5t+1=0\] \[\Rightarrow \] \[(t-1)\,(2t-1)\,[{{t}^{2}}+{{(t-1)}^{2}}]=0\] \[\Rightarrow \] \[t=1,\,\,\frac{1}{2}\] \[\Rightarrow \] \[\cos \,x=1,\,\frac{1}{2}\] \[\Rightarrow \] \[x=0,\,\,\frac{\pi }{3},\,\frac{5\pi }{3},\,2\pi \]You need to login to perform this action.
You will be redirected in
3 sec