The height #(h)# of a tree after #(n)# years is given by the equation #h=4n+7#. In how many years will the height be 39 feet?

2 Answers
Tony B
Jun 23, 2018

#n=8#

Explanation:

Set #h=39=4n+7#

Subtract 7 from both sides

#color(green)(39=4n+7color(white)("dddd")->color(white)("dddd")39color(red)(-7) =4n+7color(red)(-7))#

#color(white)("dddddddddddddd")->color(white)("ddddd")32color(white)("d")=4ncolor(white)("d")+0#

Divide both sides by 4

#color(green)(32=4ncolor(white)("ddddddd")->color(white)("dddd")32/color(red)(4)=4/color(red)(4) n)#

But #4/4# is the same as 1 and #1xxn=n# giving:

#32/4=n#

#(32-:4)/(4-:4) = 8/1=n=8#

Written as per convention

#n=8#

Jim G.
Jun 23, 2018

#8" years"#

Explanation:

#"we have to solve the equation for n"#

#4n+7=39#

#"subtract 7 from both sides"#

#4n=39-7=32#

#"divide both sides by 4"#

#(cancel(4) n)/cancel(4)=32/4rArrn=8#

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