How do you solve #x^2+x-20=0#?

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Answer 1 · 2016-03-28T14:09:04

#x=4,-5#

#color(blue)(x^2+x-20=0#

First, Factor the equation:

#rarrx^2+5x-4x-20=0#

#rarrx(x+5)-4(x+5)=0#

#color(purple)(rarr(x-4)(x+5)=0#

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#

Next, set both equations equal to zero, and solve.

#rarrx-4=0#

Add four to each side, and solve:

#rarrxcancel(-4+4)=0+4#

#color(green)(rArrx=4#

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#

#rarrx+5=0#

Subtract #5# from each side, and solve:

#rarrxcancel(+5-5)=0-5#

#color(green)(rArrx=-5#

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#

#:.color(indigo)( ul bar |x=4, -5|#