联立两个方程
r=3cosθ
r=1+cosθ
当两个相等时,3cosθ=1+cosθ
即2cosθ=1,θ=π/3和-π/3
先对心形线在-π/3到π/3的面积求出来,因为上下对称,所以面积是上面一块的两倍
S1=∫[0,π/3](1+cosθ)^2dθ=∫[0,π/3](1+2cosθ+cosθ^2)dθ=π/2+9根号3/8
对于剩下的部分就是圆r=3cosθ,从π/3积分到π/2,仍然上下对称
S2=9∫[π/3,π/2](cosθ)^2dθ=3π/4-9根号3/8
总面积S=S1+S2=3π/4-9根号3/8+π/2+9根号3/8=5π/4
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