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Factor 5x² + x − 6 | Quadratic Factoring and Discriminant Method

Sample from The Ultimate Crash Course Series
Get the full bundle with structured lessons and over 1,000 lessons and podcasts via Payhip and theSTEMmajor.com.

Factor 5x² + x − 6

5x^2+x-6=0

Start with Possible Factoring Form

(5x\pm ?)(x\pm ?)

Check Possible Combinations

(5x-2)(x-3)

(x-3)(5x-2)

(5x-3)(x-2)

(x-2)(5x-3)

(5x+2)(x-3)

(x-3)(5x+2)

(5x+3)(x-2)

(x+2)(5x-3)

Use Product of Constants

Instead of testing every possibility, examine the constant term first. The product of the final numbers must equal −6.

(-2)(3)=-6

Check the Middle Term

Now verify the coefficient of x.

(5x-2)(x+3)=5x^2+15x-2x-6=5x^2+13x-6

This does not match, so test the correct pairing.

(5x+6)(x-1)=5x^2-5x+6x-6=5x^2+x-6

Final Factored Form

(5x+6)(x-1)=0

Solutions

5x+6=0 \quad \text{or} \quad x-1=0

x=-\frac{6}{5} \quad \text{or} \quad x=1

Discriminant Check

b^2-4ac=(1)^2-4(5)(-6)=1+120=121

Since the discriminant is positive and a perfect square, the quadratic is factorable over the integers.

Conclusion

This quadratic factors cleanly, and recognizing the constant product first significantly reduces the amount of work required.

Sample from The Ultimate Crash Course Series
This lesson is part of the Ultimate Crash Course bundle. Get the full collection at Payhip and access over 1,000 lessons and podcasts through theSTEMmajor.com.
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