# 4.3. General Recursion Continued¶

This video continues exploring using recursion to implement mathematical recipes.

### Checkpoint Exercises

Power by Hand

Here is a mathematical recipe (assumes y is a positive integer) to raise x to the power of y:

Below is shown the start of evaluating 2 to the 5th power: Power(2, 5). By hand, finish the evaluation - each line should be a copy of the previous, but with the Power( ) statement on the previous line evaluated according to the recipe above.

Power(2, 5) = 2 * Power(2, 4)
= 2 * 2 * Power(2, 3)
...


We start with Power(2, 5) - x = 2 and y = 5. The recipe says that since y > 0, Power(2, 5) is really x * Power(x, y - 1) or 2 * Power(2, 4)

On the next line, we remove the Power(2, 4) and replace it with what it equals. The recipe says that if x = 2 and y = 4, then since y is > 0, the value is x * Power(x, y - 1) or 2 * Power(2, 3)

At some point, the exponent (y) should become 0. At that point, the value you replace Power( ) with will not have any more Power( )’s in it.

Since we are calculating 2 to the 5th power, your final expression better equal 32.

Power(2, 5) = 2 * Power(2, 4)
= 2 * 2 * Power(2, 3)
= 2 * 2 * 2 * Power(2, 2)
= 2 * 2 * 2 * 2 * Power(2, 1)
= 2 * 2 * 2 * 2 * 2 * Power(2, 0)
= 2 * 2 * 2 * 2 * 2 * 1
= 32


Power with BYOB:

Make a (x) to the (y) power block in BYOB using the recipe above.

You should NOT use any repeats for this task.