Давай по частям сделаем:
1) Sin420° = Sin(360° + 60°) =Sin60° = √3/2
2)Сos600° = Cos(180°*3 + 60°) = -Cos60° = -1/2
3) √3/2 * (-1/2) = -√3/4
Решение
[7*(a²)⁵] / (a² * a⁶) = (7a¹⁰)/(a⁸) = 7a²
a = √2
7*(√2)² = 7*2 = 14
1) -9.6:12=-0.8
2) 29:(-5.8)=-5
3) 4:(-25)=-0.16
4)-0.8-5-0.16=-5.96