1.(y-2)(y+2)-(y+3)(y-1),其中y=根号2.
1.(y-2)(y+2)-(y+3)(y-1),其中y=根号2.
2.(a+2b-c)(a-2b-c)
3.(a+2b)(a-2b)+(a+2b)²-4ab,其中a=1,b=十分之一.
1、原式=y2-4-y2+y-3y+3=-2y-1带入y=根号2,=-3
2、(a+2b-c)(a-2b-c)= [(a-c)+2b][(a-c)-2b]= (a-c)²-(2b)²= a² - 2ac + c² - 4b²
3、(a+2b)(a-2b)+(a+2b)²-4ab=a²-4b²+(a²+4b²+4ab)-4ab=2a²,带入a=1,原式等于2,求b
(1)
(y-2)(y+2)-(y+3)(y-1)
=y²-4-y²-2y+4
=-2y
=-2√2
(2)(a+2b-c)(a-2b-c)
=(a+c)²-(2b)²
=a²+2ac+c²-4b²
(3)(a+2b)(a-2b)+(a+2b)²-4ab
=(a+2b)(a-2b+a+2b)-4ab
=(a+2b)*2a-4ab
=2a²+4ab-4ab
=2a²
=2
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