If
∫ 0 ∞ 2 x 4 + x 2 + 1 1 d x = π a b 1 − c 1
where b is square-free, what is the value of a + b + c ?
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alright!!for those who think indefinte integral seems to be hard make substitution
x = t/ ( (2)^(0.25) ) ..Now i believe most of u can do the indefinte integral .the u will have (integral is there on RHS)
2^0.25 I = 1 / ( t^4+ t^2/sqrt2 + 1 )
2^0.25 I =(1/t^2) / ( t^2 + t^(-2) + 2^(-0.5) )
2^(1.25 )I = ( (1+1/t^2) - (1-1/t^2) )/ ( t^2 + t^(-2) + 2^(-0.5) )
Now just split it and make complete the square in denominator
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I = ∫ 0 ∞ 2 x 4 + x 2 + 1 1 d x = ∫ 0 ∞ 2 ( x 2 + 4 1 − 4 7 i ) ( x 2 + 4 1 + 4 7 i ) 1 = 7 i ∫ 0 ∞ ( x 2 + 4 1 + 4 7 i 1 − x 2 + 4 1 − 4 7 i 1 ) d x = 7 + 7 7 i 2 i ∫ 0 ∞ ( 1 + 7 i 2 x ) 2 + 1 1 d x − 7 − 7 7 i 2 i ∫ 0 ∞ ( 1 − 7 i 2 x ) 2 + 1 1 d x = 7 π i ( 1 + 7 i 1 − 1 − 7 i 1 ) = 5 6 π i ( 1 − 7 i − 1 + 7 i ) = 1 4 2 π i ( e − 2 1 tan − 1 7 − e 2 1 tan − 1 7 ) = 1 4 2 2 π sin ( 2 tan − 1 7 ) = π ( 1 4 2 4 − 2 2 2 − 1 ) = π 7 2 1 − 2 8 1 Using Euler’s formula: e i θ = cos θ + i sin θ
Therefore, a + b + c = 7 + 2 + 2 8 = 3 7 .
Reference: Euler's formula