7.(20 points) Evaluate the integrals listed below \text { a. } \int \frac{2 x^{2}}{1-6 x^{3}} d x \text { b. } \int \frac{e^{2 x}}{\sqrt{e^{4 x}+1}} d x \text { c.

} \int \frac{d x}{\sqrt{x} \sqrt{1-x}} \text { d. } \int \frac{d x}{\sqrt{x^{2}-4 x+3}}