Question 218658
Child a is 4 years older than b.  The product of their ages is 140.


The equation is x(x-4)=140


how do you solve for x?


Step 1.  Form a quadratic equation to get {{{x^2-4x=140}}}.  Then subtract 140 from both sides of the equation


{{{x^2-4x-140=140-140}}}


{{{x^2-4x-140=0}}}


{{{x^2-4x-140=(x+10)(x-14)=0}}}


Or x=-10 and x=14.  We need to select x=14 for positive ages.


ANSWER:  x is 14 hears old



Step 2.  We can also se the quadratic formula given as


{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}


where a=1, b=-4 and c=-140


*[invoke quadratic "x", 1, -4, -140 ]


Same result as before...


I hope the above steps were helpful.


For FREE Step-By-Step videos in Introduction to Algebra, please visit http://www.FreedomUniversity.TV/courses/IntroAlgebra and for Trigonometry visit http://www.FreedomUniversity.TV/courses/Trigonometry.


Good luck in your studies!


Respectfully,
Dr J