If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Algebra basics (ASL)

Course: Algebra basics (ASL) > Unit 7

Lesson 9: Solving quadratic equations by factoring (ASL)
Math
Algebra basics (ASL)
Quadratics and polynomials (ASL)
Solving quadratic equations by factoring (ASL)
© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

Solving quadratics by factoring review

Google Classroom
Factoring quadratics makes it easier to find their solutions. This article reviews factoring techniques and gives you a chance to try some practice problems.

Example 1

Find the solutions of the equation.
2, x, squared, minus, 3, x, minus, 20, equals, x, squared, plus, 34
2x2−3x−20=x2+342x2−3x−20−x2−34=0x2−3x−54=0(x+6)(x−9)=0\begin{aligned}2x^2-3x-20&=x^2+34\\\\ 2x^2-3x-20-x^2-34&=0\\\\ x^2-3x-54&=0\\\\ (x+6)(x-9)&=0\end{aligned}
↙↘x+6=0x−9=0x=−6x=9\begin{aligned}&\swarrow&\searrow\\\\ x+6&=0&x-9&=0\\\\ x&=-6&x&=9\end{aligned}
In conclusion, the solutions are x, equals, minus, 6 and x, equals, 9.
Want to see see another example? Check out this video.

Example 2

Find the solutions of the equation.
3, x, squared, plus, 33, x, plus, 30, equals, 0
3x2+33x+30=0x2+11x+10=0(x+1)(x+10)=0\begin{aligned}3x^2+33x+30&=0\\\\ x^2+11x+10&=0\\\\ (x+1)(x+10)&=0 \end{aligned}
↙↘x+1=0x+10=0x=−1x=−10\begin{aligned}&\swarrow&\searrow\\\\ x+1&=0&x+10&=0\\\\ x&=-1&x&=-10\end{aligned}
In conclusion, the solutions are x, equals, minus, 1 and x, equals, minus, 10.
Want to see see another example? Check out this video.

Example 3

Find the solutions of the equation.
3, x, squared, minus, 9, x, minus, 20, equals, x, squared, plus, 5, x, plus, 16
3x2−9x−20=x2+5x+163x2−9x−20−x2−5x−16=02x2−14x−36=0x2−7x−18=0(x+2)(x−9)=0\begin{aligned}3x^2-9x-20&=x^2+5x+16\\\\ 3x^2-9x-20-x^2-5x-16&=0\\\\ 2x^2-14x-36&=0\\\\ x^2-7x-18&=0\\\\ (x+2)(x-9)&=0 \end{aligned}
↙↘x+2=0x−9=0x=−2x=9\begin{aligned}&\swarrow&\searrow\\\\ x+2&=0&x-9&=0\\\\ x&=-2&x&=9\end{aligned}
In conclusion, the solutions are x, equals, minus, 2 and x, equals, 9.
Want to see see another example? Check out this video.

Practice

Problem 1
  • Current
Solve for x.
x, squared, plus, 14, x, plus, 49, equals, 0
x, equals
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text

Want more practice? Check out these exercises: