123k views
3 votes
Factor 3x2 - 15x - 42.

User Rpd
by
7.0k points

2 Answers

6 votes

Answer:

3(x−7)(x+2)

Explanation:

Factor out 3.

Consider x ^2−5x−14. Factor the expression by grouping. First, the expression needs to be rewritten as x^2 +ax+bx−14. To find a and b, set up a system to be solved.

Since ab is negative, a and b have the opposite signs. Since a+b is negative, the negative number has greater absolute value than the positive. List all such integer pairs that give product −14.

Calculate the sum for each pair.

The solution is the pair that gives sum −5.

Rewrite x^2 −5x−14 as (x^2 −7x)+(2x−14).

Factor out x in the first and 2 in the second group.

Factor out common term x−7 by using distributive property.

Rewrite the complete factored expression.

3(x−7)(x+2)

User Anthony Faull
by
7.6k points
4 votes
3 x^{2} - 15x - 42
(x-7)(x+2)
x-7=0 x+2=0
x=7,-2
User Ricky McMaster
by
6.8k points