Question

2x+3y=8 xy=2 find 4x+9y

Answer 1

is that 4x^2+9y^2 

y=2/x 

2x+3(2/x) = 8 

2x + 6/x = 8 
2x^2 + 6 = 8x 
x^2-4x+3=0 
(x - 1)(x - 3) 
x=1 or 3 y=2 or 2/3 

so 4x^2+9y^2 = 4+36 = 40 answer

Answer 2

We have to find 4x²+9y² not 4x+9y.
$2x+3y=8;xy=2$.
⇒$(2x+3y)^{2} = 8^{2}$
⇒$(2x) ^{2} +2*2x*3y+(3y) ^{2} =64$
⇒$4x^{2} +12xy+9y^{2}=64$
⇒$4x^{2}+9y ^{2} =64-12xy$
⇒Substituting xy as 2 we get
⇒$4 x^{2} +9 y^{2} =64-12*2=64-24=40.$
Ans:4x+9y=40.