bài 1 tính giá trị của các bieur thức sau bằng cách hợp lí 1) (-48)x72+36x(-304) 2)1-2-3-4+5-6-7-8+9-10-11-11+…+97-98-99-100 5)71×52+53/530×71-180

1) $(-48) × 72 + 36 × (-304) = (-48) × 2 × 36 + 36 × (-304) = (-96) × 36 + 36 × (-304) = 36 × [(-96) + (-304)] = 36 × (-400) = 36 × 100 × (-4) = 3600 × (-4) = -14 400$

2) $1 – 2 – 3 – 4 + 5 – 6 – 7 – 8 + 9 – 10 – 11 – 12 + … + 97 – 98 – 99 – 100$

$= (1 – 2 – 3 – 4) + (5 – 6 – 7 – 8) + (9 – 10 – 11 – 11) + … + (97 – 98 – 99 -100)$

$= (-8) + (-16) + (-24) + … + (-200)$

$= (-8) × (1 + 2 + 3 + … + 25)$

$= (-8) × \frac{25 × 26}{2}$

$= (-8) × 325$

$= -2600$

3) $\frac{71 × 52 + 53}{530 × 71 – 180} = \frac{71 × 52 + 53}{53 × 10 × 71 – 18 × 10} = \frac{71 × 52 + 53}{10 × (53 × 71 – 18)} = \frac{71 × 52 + 53}{10 × [71 × (52 + 1) – 18]} = \frac{71 × 52 + 53}{10 × (71 × 52 + 71 – 18)} = \frac{71 × 52 + 53}{10 × (71 × 52 + 53)} = \frac{1}{10}$