\(99-97-95-93-...-7-5-3-1\)
\(=99-\left(1+3+5+...+95+97\right)\)
\(=99-\left[\left(97-1\right):2+1\right]\left(97+1\right):2\)
\(=99-49.98:2\)
\(=99-2401=-2302\)
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
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
Tính nhanh: C=99-97+95-93+91-89+....7-5+3-1
99-97+95-93+......+7-5+3-1
99-97+95-93+........+7-5+3-1= ?
99−97+95−93+91−89+⋯+7−5+3−1
99-97+95-93+...+7-5+3-1
99-97+95-93+........+7-5+3-1
99-97+95-93+91-89+......+7-5+3-1
