Expression 4: left parenthesis, "x" minus 2 thirds "a" , right parenthesis squared plus left parenthesis, "y" minus 2 thirds "a" , right parenthesis squared less than or equal to left parenthesis, 1 third "a" , right parenthesis squaredx−23a2+y−23a2≤13a2
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Expression 5: "x" squared less than or equal to left parenthesis, 1 third "a" , right parenthesis squared left brace, negative "a" less than or equal to "y" less than or equal to "a" , right bracex2≤13a2−a≤y≤a
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Expression 6: "x" squared plus "y" squared equals 10 ninths "a" squared left brace, "x" "y" less than or equal to negative 1 third "a" squared , right bracex2+y2=109a2xy≤−13a2