Saturday, September 19, 2009

At a high school Algebra 2 level how do you solve x^2+4x +3 step by step?

We are asked to "solve" x^2+4x+3:


In the typical Algebra assignment you are asked to either evaluate an expression, simplify and expression, or solve an equation. Each of these, while related, involve a different approach.


We could evaluate x^2+4x+3 for a given value of x; say if x=3 then the expression has the value 3^2+4(3)+3=24.


If we are asked to simplify an expression, we strive to remove grouping symbols (parantheses, brackets, etc...) and then add/subtract like terms.


Here we are asked to "solve" x^2+4x+3. It is implied that we are to solve the general equation x^2+4x+3=0.


(a) You can factor the polynomial:


(x+3)(x+1)=0  


** One method is to rewrite the linear term as the sum of two terms where the product of the coefficients is the constant term: x^2+3x+1x+3; then factor by grouping: x(x+3)+1(x+3); use the distributive property to rewrite as (x+3)(x+1)=0 **


Now use the zero product property (if ab=0 then a=0, b=0, or a=b=0) to get:


x+3=0 ==> x=-3   x+1=0 ==> x=-1


So the solutions are x=-1 or -3


(b) You could complete the square:


x^2+4x=-3
x^2+4x+4=-3+4
(x+2)^2=1


x+2=1 or x+2=-1 


x=-1 or x=-3


(c) You could use the quadratic formula


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The solutions are x=-1 or x=-3

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