10. Упростите выражение 3/7 * x^5y^6 * (-2/3 * x^5y)^2.

3/7 * x^5y^6 * (-2/3 * x^5y)^2 = 3/7 * x^5y^6 * (4/9 * x^(5*2) * y^2) = (3*4)/(7*9) * x^(5+10) * y^(6+2) = 12/63 * x^15 * y^8 = 4/21 * x^15 * y^8