answer:From the given points A(0,1), B(3,2), we obtain overrightarrow{AB}=(3,1). Given vector overrightarrow{AC}=(-4,-3), then vector overrightarrow{BC}= overrightarrow{AC}- overrightarrow{AB}=(-7,-4). Therefore, the correct choice is boxed{A}. The process involves first finding the directed segment overrightarrow{AB}, then using overrightarrow{BC}= overrightarrow{AC}- overrightarrow{AB} to find the solution. This problem examines the representation of directed segments' coordinates and the application of the vector triangle rule; note the relationship between the coordinates of a directed segment and its endpoints, where the order cannot be reversed.

answer:**Answer:** According to the definition of a contrapositive, when m in mathbb{N}^*, the contrapositive of the proposition "If m > 0, then the equation x^2 + x - m = 0 has real roots" is: If the equation x^2 + x - m = 0 does not have real roots, then m leq 0. Therefore, the correct choice is: boxed{D}. **Analysis:** Directly use the definition of the contrapositive to write out the result and choose the option.

answer:**Analysis**: In the input statement, if multiple variables are entered at the same time, the separator between the variables is a comma. Therefore, the correct answer is boxed{text{A}}.

answer:To analyze each option and determine which one involves factorization from left to right, let's go through them one by one: **Option A**: x^{2}-x+1=xleft(x-1right)+1 - This transformation is a distribution, not factorization. Specifically, it involves distributing x across (x-1) and then adding 1. Factorization typically involves going from a form like ax^2 + bx + c directly to a product of binomials or other expressions, without intermediate addition outside the parentheses. **Option B**: (2x+3)left(2x-3yright)=4x^{2}-9y^{2} - This transformation is an example of polynomial multiplication, specifically the difference of squares formula, which is the opposite of factorization. The left side is already factored, and the right side is the expanded form. **Option C**: x^{2}+y^{2}=left(x+yright)^{2}-2xy - This transformation involves expanding (x+y)^2 to x^2 + 2xy + y^2 and then subtracting 2xy, which is an application of the binomial theorem and algebraic manipulation, not factorization. **Option D**: x^{2}+6x+9=left(x+3right)^{2} - This transformation is a perfect example of factorization. The left side, x^2 + 6x + 9, is a perfect square trinomial, and it is factored into the form left(x+3right)^2. This process involves recognizing the square of the first term (x^2), the square of the last term (9), and that the middle term (6x) is twice the product of the square roots of the first and last terms. This is a direct application of factorization. Therefore, the correct answer, which involves factorization from left to right, is: boxed{D}