Which statements are true? 1. 20 is the greatest common factor of 40 and 80.

2. 64 is a perfect square.

3. x(x^2+1)=x^3+x

4. x^2-81 cannot be factored

5. 3x^3 is the GCF of 15x^4+9x^2+3

6. (x+5) is a factor of x^2-2x+15

7. (4x^2+2)(x^2-2)=4x^4-6x^2-4

8. x+3 is a factor of x^2+9

9. The product of two binomials is always a trinomial.

10. 57 is a prime number.