Answers

2016-01-05T19:20:50+05:30
2XY=7
X=7/2Y
3X-Y=18
3*7/2Y-Y=18
21/2Y-Y=18
21-2Y²=36Y
2Y²+36Y-21=0
X=(-36+-√36²-4(2)(21))/2*2
⇒(-36+-√1296+168)/4⇒(-36+-√1464)/4⇒
0
2016-01-05T22:44:57+05:30
So we have been given 2 equations here
1)  3x - y = 18
2)  2xy = 7
in order to solve this pair of equations, we need to derive a relationship between x and y. So letus take the first equation
  3x - y = 18
taking y to RHS and 18 to LHS(keeping sign convention in mind)
we get 3x - 18 = y
so now we substitute this value of y in our second equation which was
 2xy = 7
which gives us 2x (3x - 18) =7
now upon opening the braces, we get
6 x^{2} - 36x - 7 = 0
now we need to solve the quadratic equation in x to determine the possible values of x
x = (-36+ \sqrt{1296+4(6)(7)} )/2*6
this leaves us at x = (-36 + 38.226)/12 = 0.1885
                 therby y = (3x - 18) = -17.435            
                       or x = (-36 - 38.226)/12 = 74.226
                 therby y = (3x - 18) =  204.628
P.S( what i felt after reading the question is that the aqsker mightve missed a '+' sign in the second eqn, if that is the case, then
3x - y = 18
2x + y = 7
adding both eqns, 5x = 25; x = 5
hence y = -3; which seems a lot more simpler)
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