Question 393707


Suppose you are given the sum of {{{two}}} real numbers 
first name these numbers like {{{x}}} and {{{y}}}

the sum of them you will write like {{{x + y}} and it will be equal to certain number, for example {{{10}}}

write an equation:{{{x + y = 10}}....(1)...this will be first equation

than you have the difference of these real numbers equal to certain number, let say the difference is {{{4}}}

now write the other equation

{{{x - y = 4}}}....(2)




now you have a system of two equations with two unknown variables

{{{x + y = 10}}}....(1)...

{{{x - y = 4}}}....(2)
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now take any equation of these two and solve for one variable, for example {{{x}}}

{{{x + y = 10}}}....(1)...solve for {{{x}}}

{{{x = 10 - y}}}....(1)...now substitute it in second equation 

{{{(10 - y) - y = 4}}}....(2)and solve for {{{y}}}

{{{10 - y - y = 4}}}

{{{10 - 2y  = 4}}}

{{{10 - 4  = 2y}}}

{{{6  = 2y}}}

{{{6/2  = 2y/2}}}

{{{3 = y}}}..................now you can find {{{x}}}


{{{x = 10 - y= 10 - 3 = 7}}}

so, your numbers are {{{x=7}}} and {{{y = 3}}}

check: plug in values for {{{x}}} and {{{y }}}

{{{x + y = 10}}}....(1)...

{{{7 + 3 = 10}}}

{{{10 = 10}}}


{{{x - y = 4}}}....(2)

{{{7 - 3 = 4}}}

{{{4 = 4}}}