比如我遇到一个积分式是无法具体解出来的，是不是就不能做他的图像了呢
a := int(sqrt(2*x^2+4/(-x^2+1)), x = 0 .. x)
plot(a, x = 0 .. 1)
然后一点确定，系统就提示：
Warning, unable to evaluate the function to numeric values in the region; see the plotting command's help page to ensure the calling sequence is correct