How do you solve #3x^2 -12x = 9# using the quadratic formula?

1 Answer
Jim G.
Apr 24, 2017

#x=2+-sqrt7#

Explanation:

#"rearrange terms and equate to zero"#

#rArr3x^2-12x-9=0#

#"divide all terms by 3"#

#rArrx^2-4x-3=0#

#"compare to standard form " ax^2+bx+c=0#

#"here " a=1,b=-4" and " c=-3#

#"using the " color(blue)"quadratic formula"#

#color(red)(bar(ul(|color(white)(2/2)color(black)(x=(-b+-sqrt((b^2-4ac)))/(2a))color(white)(2/2)|)))#

#rArrx=(-(-4)+-sqrt((-4)^2-(4xx1xx-3)))/(2xx1)#

#color(white)(rArrx)=(4+-sqrt(16+12))/2=(4+-sqrt28)/2#

#color(white)(rArrx)=2+-1/2sqrt28#

#color(white)(rArrx)=2+-1/2sqrt(4xx7)#

#color(white)(rArrx)=2+-sqrt7#

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