The square of a positive number is 21 more than 4 times the number. How do you find the number?

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Answer 1 · 2018-04-14T04:09:53

#x=7#

First, translate the statement into an equation:

#x^2=21+4x " "# Subtract 21 and 4x on both sides to get:

#x^2-4x-21=0 " "# Factor the quadratic to get:

#(x-7)(x+3)=0 " "# Set each factor equal to zero:

#x-7=0# and #x+3=0 " "# Solve each equation:

#x=7# and #x=-3#

Since the statement said it must be a "positive" number, we go with only 7.