先化简再求值-2(a²+1)+3(a+5)-1/2(4a²-2a),其中a=1/2…
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先化简再求值-2(a²+1)+3(a+5)-1/2(4a²-2a),其中a=1/2……
先化简再求值
(1)-2(a²+1)+3(a+5)-1/2(4a²-2a),其中a=1/2;
(2)4xy-[(x²+5xy-y²)-(x²+3xy-2y²)],其中x=1/4,y=-1/2;
(3)-2x²-1/2[3y²-2(x²-y²)+6],其中x=-1,y=-2;
(4)1/2x-2(x-1/3y²)+(-3/2x+1/3y²),其中x=-2,y=2/3
先化简再求值
(1)-2(a²+1)+3(a+5)-1/2(4a²-2a),其中a=1/2;
(2)4xy-[(x²+5xy-y²)-(x²+3xy-2y²)],其中x=1/4,y=-1/2;
(3)-2x²-1/2[3y²-2(x²-y²)+6],其中x=-1,y=-2;
(4)1/2x-2(x-1/3y²)+(-3/2x+1/3y²),其中x=-2,y=2/3
![先化简再求值-2(a²+1)+3(a+5)-1/2(4a²-2a),其中a=1/2…](/uploads/image/z/15350541-69-1.jpg?t=%26%2365279%3B%E5%85%88%E5%8C%96%E7%AE%80%E5%86%8D%E6%B1%82%E5%80%BC-2%EF%BC%88a%26%23178%3B%2B1%EF%BC%89%2B3%EF%BC%88a%2B5%EF%BC%89-1%2F2%EF%BC%884a%26%23178%3B-2a%EF%BC%89%2C%E5%85%B6%E4%B8%ADa%3D1%2F2%E2%80%A6)
(1)-2(a²+1)+3(a+5)-1/2(4a²-2a),其中a=1/2;
-2(a²+1)+3(a+5)-1/2(4a²-2a)
=-2a²-2+3a+15-2a²+a
=-4a²+4a+13
=-4×1/4+4×1/2+13
=-1+2+13
=14
(2)4xy-[(x²+5xy-y²)-(x²+3xy-2y²)],其中x=1/4,y=-1/2;
4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]
=4xy-(x²+5xy-y²-x²-3xy+2y²)
=4xy-2xy-y²
=2xy-y²
=2×1/4×(-1/2)-1/4
=-1/2
(3)-2x²-1/2[3y²-2(x²-y²)+6],其中x=-1,y=-2;
-2x²-1/2[3y²-2(x²-y²)+6]
=-2x²-1/2(5y²-2x²+6)
=-2x²-5/2y²+x²-3
=-x²-5/2y²-3
=-1-10-3
=-14
(4)1/2x-2(x-1/3y²)+(-3/2x+1/3y²),其中x=-2,y=2/3
1/2x-2(x-1/3y²)+(-3/2x+1/3y²)
=1/2x-2x+2/3y²-3/2x+1/3y²
=y²-3x
=4/9+6
=6又4/9
-2(a²+1)+3(a+5)-1/2(4a²-2a)
=-2a²-2+3a+15-2a²+a
=-4a²+4a+13
=-4×1/4+4×1/2+13
=-1+2+13
=14
(2)4xy-[(x²+5xy-y²)-(x²+3xy-2y²)],其中x=1/4,y=-1/2;
4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]
=4xy-(x²+5xy-y²-x²-3xy+2y²)
=4xy-2xy-y²
=2xy-y²
=2×1/4×(-1/2)-1/4
=-1/2
(3)-2x²-1/2[3y²-2(x²-y²)+6],其中x=-1,y=-2;
-2x²-1/2[3y²-2(x²-y²)+6]
=-2x²-1/2(5y²-2x²+6)
=-2x²-5/2y²+x²-3
=-x²-5/2y²-3
=-1-10-3
=-14
(4)1/2x-2(x-1/3y²)+(-3/2x+1/3y²),其中x=-2,y=2/3
1/2x-2(x-1/3y²)+(-3/2x+1/3y²)
=1/2x-2x+2/3y²-3/2x+1/3y²
=y²-3x
=4/9+6
=6又4/9
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