Identify the values of a, b and c for the given quadratic trinomial in its standard form. Find two factors of ac whose sum is equal to b.
(5x-1)(x-5)
Practice makes perfect
We want to completely factor the given expression. Here we have a quadratic trinomial of the form ax^2+bx+c, where |a| ≠1 and there are no common factors. To factor this expression, we will rewrite the middle term, bx, as two terms. The coefficients of these two terms will be factors of ac whose sum must be b.
5x^2-26x+5 ⇔ 5x^2+( - 26)x+ 5
We have that a= 5, b= - 26, and c= 5. There are now three steps we need to follow in order to rewrite the above expression.
Find a c. Since we have that a= 5 and c= 5, the value of a c is 5* 5=25.
Find factors of a c. Since a c=25, which is positive, we need factors of a c to have the same sign — both positive or both negative — in order for the product to be positive. Since b= - 26, which is negative, those factors will need to be negative so that their sum is negative.
We can see above that after expanding and simplifying, the result is the same as the given expression. Therefore, we can be sure our solution is correct!
