计算题:(1)99×101 (公式法)(2)(4x2y+5xy﹣7y)﹣(5x2y﹣4xy+x)(3)(x﹣2y)2+4(x﹣y)(x+y);(4)(a+2b﹣
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计算题: (1)99×101 (公式法) (2)(4x2y+5xy﹣7y)﹣(5x2y﹣4xy+x) (3)(x﹣2y)2+4(x﹣y)(x+y); (4)(a+2b﹣c)(a+2b+c) (5)(2x3y4z2+4x3y3z3﹣6x2y3z5)÷(2x2yz2) (6)(x+3y)(x﹣2y)﹣x3÷x+6y2,其中x=2,y=﹣3 |
答案
解:(1)原式=(100﹣1)(100+1), =1002﹣1, =10000﹣1, =9999; (2)(4x2y+5xy﹣7y)﹣(5x2y﹣4xy+x), =4x2y+5xy﹣7y﹣5x2y+4xy﹣x, =(4﹣5)x2y+(5+4)xy﹣7y﹣x, =﹣x2y+9xy﹣7y﹣x; (3)(x﹣2y)2+4(x﹣y)(x+y), =x2﹣4xy+4y2+4x2﹣4y2, =5x2﹣4xy; (4)设:a+2b=m, 则原式(a+2b﹣c)(a+2b+c)=(m﹣c)(m+c), =m2﹣c2, ∵a+2b=m, ∴m2﹣c2=(a+2b)2﹣c2, =a2+4ab+4b2﹣c2; (5)(2x3y4z2+4x3y3z3﹣6x2y3z5)÷(2x2yz2), =2x3y4z2÷2x2yz2+4x3y3z3÷2x2yz2﹣6x2y3z5÷2x2yz2, =xy3+2xy2z﹣3y2z3; (6)(x+3y)(x﹣2y)﹣x3÷x+6y2, =x2+xy﹣6y2﹣x2+6y2, =xy, 当x=2,y=﹣3时,原式=2×(﹣3)=﹣6 |
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