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Question
If Φ(x)=dxsin12x cos72x, then Φ(π4)Φ(0)=
Options:
A .  125
B .  95
C .  65
D .  0
Answer: Option A
:
A
tanx=tsec2xdx=dtf(x)=dxsin12xcos12x.cos4x=(1+tan2x)sec2xtanxdx=(1+t2)tdt=(t1/2+t3/2)dt=2t1/2+25t5/2=2tanx+25(tanx)5/2ϕ(π4)ϕ(0)=2+25=125

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