Đáp án:
A=1.2²+2.3²+3.4²+....98.99²
⇒2A=2.3²+3.4²....99.100²
⇒A=2A−A=1.2²+2.3²+3.4²+....98.99²−2.3²+3.4²...99.100²
⇒A=1−100²=−99²
⇒A=1−1002=−992A=1.22+2.32+3.42+....98.992⇒2A=2.32+3.42....99.1002⇒A=2A-A=1.22+2.32+3.42+....98.992-2.32+3.42....99.1002⇒A=1-1002=-992
⇒A=1−1002=−992A=1.22+2.32+3.42+....98.992⇒2A=2.32+3.42....99.1002⇒A=2A-A=1.22+2.32+3.42+....98.992-2.32+3.42....99.1002⇒A=1-1002=-992
⇒A=1−1002=−992A=1.22+2.32+3.42+....98.992⇒2A=2.32+3.42....99.1002⇒A=2A-A=1.22+2.32+3.42+....98.992-2.32+3.42....99.1002⇒A=1-1002=-992
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