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Using numbers and the number line, show how you can perform subtraction, multiplication, division, and exponents using just addition as your only operator

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2 Answers

1) Subtraction: This is the same as adding the negative value of the number; or using the additive inverse. So the additive inverse of a real number a, is -a. Thus( x-y-x-a-b )= x + -y + -x + -a + -b

2) Multiplication: both numbers on the number line are all Real Numbers: say we have pi*x = sqrt(2)*y x,y,pi and sqrt(2) are real numbers we get infinite series for pi and sqrt 2.

pi*x and sqrt(2)*y =(infinite sums of terms for pi)*x = (infinite sums for sqrt(2)*y =

Infinite sum of (pi*x) + infinite sum (sqrt(2)*y)

x, y are constant values, the infinite sum terms are constants

So we have turned multiplication of two reals = two reals = sum1 = sum2

4) Division (real numbers a,b,c,d, known)

such that a/b = c/d -> the integer value of a/b terms (1 + 1 + 1 +1…) + remainder term a/b*1 =

integer value of c/d terms of 1 + 1 + 1…+remainder pf cd*1

so a/b = c/d becomes 1 + 1 + 1 + … + rem(a/b) *1= 1 + 1 + 1 +…+ rem(c/d)*1

So here the division turns into addition for all real numbers

 

This is a great question!  I'll be glad to help.

Subtraction: To subtract by adding, just add negative numbers and thus move left on the number line (subtracting) instead of moving right (adding).

     Example: 2 - 3 = 2 + (-3) = -1                                                                                                    You start at 2 on a number line and move to the left three numbers.

Multiplication: To multiply by adding, you add the first number to itself the same number of times as the second number.

     Example: 2 x 3 = 2 + 2 + 2 = 6. Notice that you add three 2's together which is the same as 2 x 3.   The same works for multiplying by a negative number, in which case you will end up adding negative numbers (see subtracting above) instead of positive.  Try it yourself!

     Example two: The tricky situation is when you mutiply two negative numbers together, so let's try one. One negative number is easy: -2 x 3 = -2 + -2 + -2 = -6. BUT, look at this: -2 x -3 = -(-2) -(-2) -(-2) = 2 + 2 + 2 = 6.  See how you subtract -2 instead of adding -2.  We do this because we must do the opposite of what a positive 3 would tell us to do; since -3 is the opposite of 3 when we are using addition as our operator.  As long as you remember that a negative number times a negative number makes a positive, this should make sense.  If not, let me know and I'll explain this a different way.

Division: To divide, change the problem into a multiplication problem and then follow the mulitplication example above.

     Example: 8 / 2 = 8 x (1/2) = (1/2) + (1/2) + (1/2) + (1/2) + (1/2) + (1/2) + (1/2) + (1/2) = 4. Notice how you add eight (1/2)'s together which is the same as 8 / 2.  Again, this works when one of the numbers is negative as well.

Exponentiation: Similar to division, we are dealing with another disguise.  Exponentiation is a multiplication problem in diguise, and as we know from above, multiplication is addition in disguise. (Below the carrot, "^", is used before any number used as an exponent)

     Example: 2^3 = 2 x 2 x 2 = (2 x 2) x 2 = (2 + 2) x 2= 4 x 2 = 4 + 4 = 8 After some rewriting in steps two and three, step four multiplies 2 by 2 meaning you add two 2's together.  Then you take the resulting 4 and multiply it by 2 meaning you add two 4's together.

If the base number is a negative, you will have to follow the second example of multiplication.  But, the real tricky one here is when the exponent is negative.

     Example 2: 2^-3.  You have to change the negative power to a positive power by putting the base in the denominator: 2^-3 = 1/(2^3).  After that, you should be able to follow other examples above: 1/(2^3) = 1/((2 x 2) x 2) = 1/((2 + 2) x 2) = 1/(4 x 2) = 1/(4 + 4) = 1/8 = 1 x (1/8) = 1/8.  The last step you add 1/8 one time, meaning you essentially don't add anything and you stay at the same spot on the number line, at 1/8, which is the answer.  

Please let me know if any of this is hard to understand.  This question is great and I would welcome the chance to disucss it more!

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