Question

初一数学：先化简，再求值（1）8p²-7q+6q-7p²-7，其中p=3,q=-1

(2)-9y+6x²+3(y-2/3x²）其中x=2,y=-1

Answer 1

8p²-7q+6q-7p²-7
=p²-q-7 p=3,q=-1
=3²+1-7
=3

-9y+6x²+3(y-2/3x²）
=-9y+6x²+3y-2x²
=4x²-6y
=2(x²-3y)
=2(2²+3)
=2×7
=14
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Answer 2

（1）8p²-7q+6q-7p²-7，其中p=3,q=-1
8p²-7q+6q-7p²-7
=p²-q-7
=9+1-7
=3

(2)-9y+6x²+3(y-2/3x²）其中x=2,y=-1
-9y+6x²+3(y-2/3x²)
=-9y+6x²+3y-2x²
=4x²-6y
=16+6
=22

Answer 3

（1）8p²-7q+6q-7p²-7=(8p²-7p²)+(-7q+6q)-7=p²-q-7=9-(-1)-7=10-1=3

(2)-9y+6x²+3(y-2/3x²）=(-9y+3y)+(6x²-2x²)=-6y+4x²=-6*(-1)+4*2²=6+16=22

Answer 4

8p²-7q+6q-7p²-7
=p²-q-7 （带入 p=3,q=-1）
=3²+1-7
=3

-9y+6x²+3(y-2/3x²）
=-9y+6x²+3y-2x²
=4x²-6y
=2(2x²-3y) （带入x=2,y=-1）
=2(2·2²+3)
=2×11
=22

Answer 5

8p2-7p2-7q+6q-7 =p2-q-7 把那俩数代入