If Σkr=1cos−1βr=kπ2 for any k≤1 and A=Σkr=1(βr)r, then limx→A(1+x)1/3−(1−2x)1/4x+x2 is equal to
A
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B
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C
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D
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Solution
The correct option is D ∵Σkr=1cos−1βr=kπ2Whichispossiblebywhencos−1β1=cos−1β2=cos−1β3=……=cos−1βk=π2∴β1=β2=β3=……=βk=0Hence,A=Σkr=1(βr)r=0∴limx→0(1+x)1/3−(1−2x)1/4x+x2⇒limh→0((1+x)1/3−(1)1/3(1+x)−1)((1−2x)1/4−(1)1/4(1−2x)−1×(−2))(1+x)⇒12+2×141+0=13+12=56