No of solutions of equation tanx+secx=2cosx, x∈[0,2π] is
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a
1
b
2
c
3
d
4
answer is B.
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Detailed Solution
tanx+secx=2cosx⇒sinxcosx+1cosx=2cosx⇒sinx+1=2cos2x⇒sinx+1=2(1−sin2x)⇒2sin2x+sinx−1=0⇒2sin2x+2sinx−sinx−1=0⇒2sinx(sinx+1)−1(sinx+1)=0⇒(2sinx−1)(sinx+1)=0⇒sinx=12 or sinx=−1⇒sinx=sinπ6or sinx=sin−π2⇒x=nπ+(−1)nπ6or x=2nπ-π2⇒for n=0,x=π6, x=−π2 for n=1,x=π−π6=5π6 , x=2π−π2=3π23π2 does not satisy the given equation for n=2,x=2π+π6 , x=2π−π2=7π2∴x=π6,5π6∈0,2π are the only solutions