Giải bài 2 (6. 45) trang 24 vở thực hành Toán 6 Q2 — Không quảng cáo

Đề bài

Bài 2 (6.45). Tính một cách hợp lí:

a) $A = \frac{{ - 3}}{{14}} + \frac{2}{{13}} + \frac{{ - 25}}{{14}} + \frac{{ - 15}}{{13}}$

b) $B = \frac{5}{3}.\frac{7}{{25}} + \frac{5}{3}.\frac{{21}}{{25}} - \frac{5}{3}.\frac{7}{{25}}$

Lời giải chi tiết

a) $A$ $= \frac{{ - 3}}{{14}} + \frac{2}{{13}} + \frac{{ - 25}}{{14}} + \frac{{ - 15}}{{13}}$ $= \left( {\frac{{ - 3}}{{14}} + \frac{{ - 25}}{{14}}} \right) + \left( {\frac{2}{{13}} + \frac{{ - 15}}{{13}}} \right)\\ $ $= \frac{{ - 28}}{{14}} + \frac{{ - 13}}{{13}}$ $=  - 2 - 1$ $=  - 3$

b) $B$ $= \frac{5}{3}.\frac{7}{{25}} + \frac{5}{3}.\frac{{21}}{{25}} - \frac{5}{3}.\frac{7}{{25}}$ $= \frac{5}{3}.\left( {\frac{7}{{25}} + \frac{{21}}{{25}} - \frac{7}{{25}}} \right)\\ $ $= \frac{5}{3}.\left( {\frac{7}{{25}} - \frac{7}{{25}} + \frac{{21}}{{25}}} \right)$ $= \frac{5}{3}.\frac{{21}}{{25}}$ $= \frac{7}{5}$