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Explanation:
[tex]f(x)= -13x^2+15\\\\f(x)= -13x^2+15*1\\\\f(x)= -13x^2+15x^0\\\\[/tex]
Each term of the polynomial function has an exponent which is an even number, therefore the function is even.
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Another approach:
[tex]f(x)= -13x^2+15\\\\f(-x)= -13(-x)^2+15\\\\f(-x)= -13x^2+15\\\\[/tex]
Since f(x) = f(-x) for all x, this proves the function is even.