How is the Power Spectrum of Matter Density Field Defined?

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Homework Statement
The definition of power spectrum of matter density field is given by eq (1). I have also seen definitions of power spectra given by eq (2) . Does this mean ##(2\pi^3)## has been absorbed in the correlation function?
Relevant Equations
##P_{xx}(k)=(2\pi^3)\delta(k-k^\prime)\langle x(k)x(k^\prime)\rangle##

##P_{yy}(k)=\delta(k-k^\prime)\langle y(k)y(k^\prime)\rangle##

<Mentor: edit latex>
The definition of power spectrum of matter density field is given by eq(1). I have also seen definitions of power spectra given by eq(2) . Does this mean (2\pi^3) has been absorbed in the correlation function?

$$P_{xx}(k)=(2\pi^3)\delta(k-k^\prime)<x(k)x(k^\prime)>$$ .. (1)
$$P_{yy}(k)=\delta(k-k^\prime)<y(k)y(k^\prime)> $$.. (2)
 
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