For rational numbers p and q , the area of the shaded region is equal to p + q π .
Find 4 q p .
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How did you decide for the substitution x = 2 1 ( 1 + 3 tan ϕ ) ?
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It should be x = 2 1 ( 1 + 3 tan ϕ ) (I have corrected the proof), and it is used because x 2 − x + 1 = ( x − 2 1 ) 2 + 4 3 .
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The polar equation of the curve is 1 = r ( cos 3 θ + sin 3 θ ) for 0 ≤ θ ≤ 2 1 π . Thus the desired area is A = 2 1 ∫ 0 2 1 π ( sin 3 θ + cos 3 θ ) 2 d θ = 2 1 ∫ 0 2 1 π ( 1 + tan 3 θ ) 2 sec 6 θ d θ = 2 1 ∫ 0 ∞ ( 1 + x 3 ) 2 ( 1 + x 2 ) 2 d x = 1 8 1 ∫ 0 ∞ ( 1 + x 2 + 1 − x + x 2 1 + x ) 2 d x = 1 8 1 ∫ 0 ∞ ( ( 1 + x ) 2 4 + 1 − x + x 2 4 + ( 1 − x + x 2 ) 2 ( 1 + x ) 2 ) d x = 1 8 1 ∫ 0 ∞ ( ( 1 + x ) 2 4 + 1 − x + x 2 5 + ( 1 − x + x 2 ) 2 3 x ) d x = 1 8 1 [ − 1 + x 4 + 3 1 0 tan − 1 ( 3 2 x − 1 ) − 2 ( x 2 − x + 1 ) 3 ] 0 ∞ + 1 2 1 ∫ 0 ∞ ( x 2 − x + 1 ) 2 d x = 3 6 1 1 + 2 7 3 1 0 π + 1 2 1 ∫ 0 ∞ ( x 2 − x + 1 ) 2 d x The substitution x = 2 1 ( 1 + 3 tan ϕ ) now gives A = 3 6 1 1 + 2 7 3 1 0 π + 9 3 2 ∫ − 6 1 π 2 1 π cos 2 ϕ d ϕ = 3 6 1 1 + 2 7 3 1 0 π + 9 3 1 ∫ − 6 1 π 2 1 π ( cos 2 ϕ + 1 ) d ϕ = 3 6 1 1 + 2 7 3 1 0 π + 9 3 1 [ 2 1 sin 2 ϕ + ϕ ] − 6 1 π 2 1 π = 3 1 + 9 3 4 π so that p = 3 1 and q = 2 4 3 1 6 . Thus 4 q p = 9 .