Question #d2d79

1 Answer
Jul 29, 2017

Answer:

#x = 65+sqrt2125 = 111.1#

#x= 65-sqrt2125 =18.9#

Explanation:

You have got to the step of #1425 = (125-x)(x-5)#

Now get rid of the brackets, and you will end up with an #x^2# term.
That means it is a quadratic equation.

Make it equal to #0# and then decide on an appropriate method of solving..

#color(white)(xxxxxxxxxxxxx)1425 = (125-x)(x-5)#

#color(white)(xxxxxxxxxxxxx)1425 = 125x-625 -x^2 +5x#

#x^2 -130x +625 + 1475 =0#

#color(white)(xxxxx) x^2-130x +2100 =0#

Complete the square:

#x^2 -130x color(white)(xxxx) = -2100" "larr ((-160)/2)^2 = 65^2#

#x^2 -130x +65^2 = -2100 +65^2#

#(x-65)^2 = 2,125#

#x-65 = +-sqrt2125#

#x = 65+sqrt2125 = 111.1#

#x= 65-sqrt2125 =18.9#