Question 943443
f(x) is even when f(-x) = f(x) for all x in the domain.



f(x) = mx + b



f(-x) = m(-x) + b



f(-x) = -mx + b



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Set f(-x) equal to f(x)



f(-x) = f(x)



-mx + b = mx + b



-mx + b<font color="red">-b</font> = mx + b<font color="red">-b</font> <font color="blue"> ... Subtract b from both sides.</font>



-mx = mx



-mx<font color="red">+mx</font> = mx<font color="red">+mx</font><font color="blue"> ... Add mx to both sides.</font>



0 = mx+mx



0 = 2mx



2mx = 0



2mx = 0 means m = 0 (since x is any number, it's not always 0, so m has to be zero)