先化简,再求值:(x+5)²-(x-5)²-5(2x+1)(2x-1)+x(2x)²
其中x=-1
解:
化简:
原式=(x+5)²-(x-5)²-5(2x+1)(2x-1)+x(2x)²
=10x+10x-20x²+5+4x³
=4x³-20x²+20x+5
x=-1代入得:
原式=-4-20-20+5=-39
赋值:
原式=4²-6²-5×(-1)(-3)-4
=-39
(x+5)²-(x-5)²-5(2x+1)(2x-1)+x(2x)²
=(x²+10x+25)-(x²-10x+25)-5(4x²-1)+x(4x²)
=x²+10x+25-x²+10x-25-20x²+5+4x³
=4x³+x²-x²-20x²+10x+10x+25-25+5
=4x³-20x²+20x+5
=4(-1)³-20(-1)²+20(-1)+5
=-1-20-20+5
=-36
(x+5)²-(x-5)²-5(2x+1)(2x-1)+x(2x)²
=(2x)(5+5)-5(4x²-1)+2x³
=20x-20x²+5+2x³
其中x=-1,代入上式得
-20-20+5-2
=-37
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