Basic Optical Principles
Mathematics Review

Addition Of A Plus And Minus Number: The sign of the answer will always be the same as the sign of the higher of the two numbers you are adding. A good rule to remember is as follows: when adding two numbers of opposite signs, subtract the smaller number from the larger number, then give the answer the sign of the larger number.

Examples:

+10.25  – 8.50 +1.75

–3.50 +4.75 +1.25

+3.00 -7.00 -4.00

May Also Be Written:

+10.25 – 8.50 = +1.75
– 3.50 + 4.75 = +1.25
+ 3.00 � 7.00 = �4.00

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Algebraic Addition As A Function of Direction:

Addition in algebra is a function of direction. Consider a thermometer. All numbers above the zero are plus and those below the zero are minus. If the temperature is three degrees above zero, then drops to two degrees below zero, the temperature has changed by five degrees. Or, stated another way, +3.00 -5.00 = -2.00.