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# x^2+8x-20=0 Solve using any method

### 2 Answers by Expert Tutors

Michael W. | Experienced Biology teacher/tutor/nestorExperienced Biology teacher/tutor/nestor
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Hi! Since the coefficient of the x^2 is 1 (1x^2), you have a quick method to do this.
First identify the factors of 20 in pairs (20*1, 10*2, 5*4)

Now which pair when added or subtracted from each other gives you 8?
20+1=21, 20-1=19, 10+2=12, 10-2=8, 5+4=9, 5-4=1

You need the 10 and 2.

One must be negative so that when multiplied, you get a -20 as a result. However, when added or subtracted, you need to get a positive 8. Therefore the 2 is negative (10+ (-2) = 8)

Hope this helps

Mike
Philip P. | Effective and Affordable Math TutorEffective and Affordable Math Tutor
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x^2+8x-20=0 Solve using any method

Easiest Method - Factoring:

To factor, you need two numbers that multiply together to give -20 and add together to give 8.

Multiples of -20 are ±20*±1, ±10*±2, ±5*±4.  Let's try +10 and -2:

10 + (-2) = 8
10*(-2) = -20

10 and -2 work, so:

x2+8x-20 = (x+10)(x-2) = 0

so x = -10 and 2