Карточка 3: 1) 21c/(28c⁴) =; 2) 8m⁵n²/(12m²n) =; 3) (z²−81)/(z−9) =; 4) (9f−18)/(18f−36) =; 5) (x²+3x)/(x²−9) =; 6) (3s+15)/(s²+5s) =.

1. \(\dfrac{21c}{28c^4}=\dfrac{3}{4c^3}\).
2. \(\dfrac{8m^5n^2}{12m^2n}=\dfrac{2m^3n}{3}\).
3. \(\dfrac{z^2-81}{z-9}=\dfrac{(z-9)(z+9)}{z-9}=z+9\).
4. \(\dfrac{9f-18}{18f-36}=\dfrac{9(f-2)}{18(f-2)}=\dfrac12\).
5. \(\dfrac{x^2+3x}{x^2-9}=\dfrac{x(x+3)}{(x-3)(x+3)}=\dfrac{x}{x-3}\).
6. \(\dfrac{3s+15}{s^2+5s}=\dfrac{3(s+5)}{s(s+5)}=\dfrac3s\).

Ответ: 1) \(\frac3{4c^3}\); 2) \(\frac{2m^3n}{3}\); 3) \(z+9\); 4) \(\frac12\); 5) \(\frac{x}{x-3}\); 6) \(\frac3s\).