一个很好的数学公式网站

buddyk

http://www.gomath.com/formulatogo.html

哪位大虾最近不考有空，去整理一下，贴到论坛来：）

谢谢！

LES

谢谢buddyk提供分享！

saiever

Rules for Addition

Rules for Addition	Examples
If a and b are both positive, then a + b = |a| + |b|	3 + 7 = 10
If a and b are both negative, then a + b = -(|a| + |b|)	-6 + (-2) = -(6 + 2) = -8
If a is positive and b is negative and a has the greater absolute value, then a + b = |a| - |b|	8 + (-5) = 8 - 5 = 3
If a is positive and b is negative and b has the greater absolute value, then a + b = -(|b| - |a|)	4 + (-9) = -(9 - 4) = -5
If a and b are opposites, then a + b = 0	2 + (-2) = 0

ppyy

Negative Numbers Addition

Rule	Example
Positive Number + Positive = Positive Number	7 + 4 = 11 2 + 15 = 17
Negative Number + Negative Number = Negative Number	-4 + (-9) = -(4 + 9) = -13 -12 + (-43) = -(12 + 43) = -55
Positive + Negative OR Negative + Positive case 1: The positive number is larger: Answer = Positive case 2: The negative number is larger: Answer = Negative	case 1: 14 + (-5) = 14 - 5 = 9 case 2: -19 + 7 = -(19 - 7) = -12

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