A) 1
B) 2
C) 3
D) 4
Correct Answer: D
Solution :
Given, \[3\cos 2x-10\cos x+7=0\] \[\Rightarrow 3(2{{\cos }^{2}}x-1)-10\cos x+7=0\] \[\Rightarrow \] \[6{{\cos }^{2}}x-10\cos x+4=0\] \[\Rightarrow \] \[2[(3\cos x-2)(\cos x-1)]=0\] \[\Rightarrow \] \[\cos x=1\] and \[\cos x=\frac{2}{3}\] Since, \[\cos x\]is positive in 1st and \[\text{IVth}\] quadrants. Hence, total number of solutions is 4.You need to login to perform this action.
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