（1）（3x-2y)^2=9x^2+(?)-(?)(2)(-3a^2-b)^2=(?)+b^2+(?)(3)(?+2c)^2=25t^2+4c^2+(?)(4)(?+1/2a)^2(4)(?+1/2a)^2=?+1/4a^2-ab

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