How do you factor #x^2+4x=21#?

1 Answer
Jim G.
May 18, 2017

#(x+3)(x-7)#

Explanation:

#"rearrange and equate to zero"#

#rArrx^2+4x-21=0#

#"to factor we can 'split' the middle term"#

#rArrx^2+4x-21#

#=x^2+3x-7x-21#

#"taking out a common factor gives"#

#=color(red)(x)(x+3)color(red)(-7)(x+3)#

#"take out " (x+3)" as a common factor"#

#=(x+3)(color(red)(x-7))#

#rArrx^2+4x-21=(x+3)(x-7)#

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