Answer :
Answer: The value of x- 2y is a. [tex]\pm 3[/tex].
Step-by-step explanation:
Given: x and y are two positive real numbers such that [tex]x^2+4y^2=17[/tex] and [tex]xy= 2[/tex] .
Consider [tex](x-2y)^2=x^2-2(x)(2y)+(2y)^2\ \ \ [(a+b)^2=(a^2-2ab+b^2)][/tex]
[tex]=x^2-4xy+4y^2[/tex]
[tex]=x^2+4y^2-4(xy)[/tex]
Put [tex]x^2+4y^2=17[/tex] and [tex]xy= 2[/tex] , we get
[tex](x-2y)^2=17-4(2)=17-8=9[/tex]
[tex]\Rightarrow\ (x-2y)^2=9[/tex]
Taking square root on both sides , we get'
[tex]x-2y= \pm3[/tex]
Hence, the value of x- 2y is a. [tex]\pm 3[/tex].