S = 99 – 97 + 95 – 93 + 91 – 89 + ….+11 – 9 + 7 – 5 + 3 – 1S = 99 – 97 + 95 – 93 + 91 – 89 + ….+11 – 9 + 7 – 5 + 3 – 1
A) 1×5+5×9+9×13+...89×93+93×97
B) 1×3+3×5+5×7+....95×97+97×99
C) 1×3+5×7+9×11+..93×95+97×99
Tính nhanh: C=99-97+95-93+91-89+....7-5+3-1
99−97+95−93+91−89+⋯+7−5+3−1
99-97+95-93+91-89+......+7-5+3-1
Tính nhanh
a) 99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5 + 3 - 1
b) 991 - 981 + 971 - 961 + ... + 31 - 21 + 11 - 1
99-97+95-93+91-89+.......+7-5+3-1
99-97+95-93+91-89+...+7-5+3-1
99-97+95-93+91-89+.....+7-5+3-1 = ?
