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If `I_(n)=int_(0)^(pi//4) tan^(n)x dx, (ngt1` is an integer ), thenA. `I_(n)+I_(n-2)=1/(n+1)`B. `I_(n)+I_(n-2)=1/(n-1)`C. `I_(2)+I_(4),I_(6),…….` are in H.P.D. `1/(2(n+1))ltI_(n)lt1/(2(n-1))` |
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Answer» Correct Answer - B::C::D `I_(n)=int_(0)^(pi//4)tan^(n)xdx` `=int_(0)^(pi//4)tan^(n-2)xtan^(2)xdx` `=int_(0)^(pi//4)sec^(2)x tan^(n-2)x dx-int_(0)^(pi//4) tan^(n-2) xdx` `=int_(0)^(1)t^(n-2)dt=I_(n-2)`, where `t=tanx` `:.I_(n)+I_(n-2)=((t^(n-1))/(n-1))_(0)^(1)=1/(n-1)` Thus `I_(2)+I_(4)+I_(4)+I_(6)..............` are in H.P. For `0lt xlt pi//4` we have `0 lt tan^(n-2)x` So `0ltI_(n)ltI_(n-2)` or `I_(n)+I_(n+2)lt 2I_(n)ltI_(n)+I_(n-2)` or `1/(n+1)lt 2I_(n) lt 1/(n-1)` or `1/(2(n+1)) lt I_(n) lt 1/(2(n-1))` |
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