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發問:
Expand the following expression.要step Use : (a+b)(a-b)?a^2-b^2 ，(a+b)^2?a^2+2ab+b^2 ，(a-b)^2?a^2-2ab+b^2 1.y^2-14y+48 2.12x^2-3y^2-8x+2y(The expression cannot be factorized.)(I want Explain.) 3.108^2-16*108+63
最佳解答:
1.y^2-14y+48 =y^2-(6+8)y+6*8 =(y-6)(y-8) 2.12x^2-3y^2-8x+2y(The expression cannot be factorized.)(I want Explain.) put f(x)=12x^2-8x-3y^2+2y discriminant = 64-4(12)(-3y^2+2y) = 64+48(3y^2-2y) = 64+144y^2-96y = 144(y^2-2/3y+4/9) = 144(y^2-2/3y+1/9-1/9+4/9) = 144[(y-1/3)^2+3/9] = 144[(y-1/3)^2+1/3] = 144(y-1/3)^2+48 = 12^2(y-1/3)^2+48
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