= (99 - 97 ) + (95 - 93 ) + ... + (7-5 )+ ( 3 - 1 )
= 2 + 2 + ... + 2 + 2 ( 25 số 2 )
= 2 . 25
= 50
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Các câu hỏi tương tự
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
c) 99-97-95-93-...-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
99-97+95-93+91-89+.......+7-5+3-1