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# Worked example: Evaluating functions from equation

CCSS.Math:

## Video transcript

the function f of X is defined as f of X is equal to 49 minus x squared find the value of f of 5 so whenever you're dealing with a function you take your input in this case our input is going to be our 5 we input it into our little function box and we need to get our output and they define the function box here's whatever your input is take that square it and then subtract it from 49 so f of 5 f of 5 every time I see an X here since f of X is equal to this every time I see an X I would replace it with the input so f of 5 is going to be equal to 49 minus instead of writing x squared I would write 5 squared so this is equal to 49 minus 25 and 49 minus 25 is equal to 24 and we are done