帮我算算这几题,一:(-2x²)³÷(-x)² 二:(-2m-1)(3m-2)三:(x-y)²+(2x-y)(2x-y)-2(2x²+xy),其中x=-1,y=1/4
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![帮我算算这几题,一:(-2x²)³÷(-x)² 二:(-2m-1)(3m-2)三:(x-y)²+(2x-y)(2x-y)-2(2x²+xy),其中x=-1,y=1/4](/uploads/image/z/11429720-8-0.jpg?t=%E5%B8%AE%E6%88%91%E7%AE%97%E7%AE%97%E8%BF%99%E5%87%A0%E9%A2%98%2C%E4%B8%80%EF%BC%9A%EF%BC%88-2x%26%23178%3B%EF%BC%89%26%23179%3B%C3%B7%28-x%29%26%23178%3B+%E4%BA%8C%EF%BC%9A%28-2m-1%29%283m-2%29%E4%B8%89%EF%BC%9A%28x-y%29%26%23178%3B%2B%282x-y%29%282x-y%29-2%282x%26%23178%3B%2Bxy%29%2C%E5%85%B6%E4%B8%ADx%3D-1%2Cy%3D1%2F4)
帮我算算这几题,一:(-2x²)³÷(-x)² 二:(-2m-1)(3m-2)三:(x-y)²+(2x-y)(2x-y)-2(2x²+xy),其中x=-1,y=1/4
帮我算算这几题,
一:(-2x²)³÷(-x)²
二:(-2m-1)(3m-2)
三:(x-y)²+(2x-y)(2x-y)-2(2x²+xy),其中x=-1,y=1/4
帮我算算这几题,一:(-2x²)³÷(-x)² 二:(-2m-1)(3m-2)三:(x-y)²+(2x-y)(2x-y)-2(2x²+xy),其中x=-1,y=1/4
解一题
(-2x²)³÷(-x)²
=[(-2)³×x^(2×3)]÷x²,^是乘方
=(-8x^6)÷x²
=-8x^(6-2)
=-8x^4
解二:多项式乘多项式,用其中一个多项式的每一项去乘另一个多项式的每一项,再把积相加
(-2m-1)(3m-2)
=-2m×3m+(-2m)×(-2)+(-1)×3m+(-1)×(-2)
=-6m²+4m-3m+2
=-6m²+m+2
解三题:
原式=(x-y)(x-y)+(2x-y)(2x-y)-2(2x²+xy)
=x×x+x×(-y)+(-y)×x+(-y)×(-y)+2x×2x+2x×(-y)+(-y)×2x+(-y)×-y)-4x²-4xy
=x²-2xy+y²+4x²-4xy+y²-4x²-4xy
=x²-10xy+2y²
当x=-1,y=1/4时
原式=(-1)²-10×(-1)×1/4+2×(1/4)²
=1+5/2+1/8
=8/8+20/8+1/8
=29/8