kak tolong dong, yg no 2 dan 3

2. a. 1+3+5+7+9+99
= (1+99)²/2=100²/2=50²=2.500
b. 1-2+3-4+5-6+7-8+...-100
=(-1)+(-1)+(-1)+(-1)-100
=(-4)-100
=96

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