表达式13: polygon left parenthesis, negative 20 plus 2 "x" Subscript, 1 , Baseline , 20 minus 4 "y" Subscript, 1 , Baseline , right parenthesispolygon−20+2x1,20−4y1
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表达式14: polygon left parenthesis, negative 10 "t" Subscript, 1 , Baseline plus 2 "x" Subscript, 1 , Baseline , 20 minus 4 "y" Subscript, 1 , Baseline , right parenthesispolygon−10t1+2x1,20−4y1
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表达式15: polygon left parenthesis, negative 10 minus 10 left parenthesis, 1 minus "t" Subscript, 1 , Baseline , right parenthesis plus 2 "x" Subscript, 1 , Baseline , 20 minus 4 "y" Subscript, 1 , Baseline , right parenthesispolygon−10−101−t1+2x1,20−4y1
