Question

If

9x^2+y^2= 58 , xy=7

Then

3x+y=?

Answer 1

Hi friend,

Please refer the pic.

Hope it helps..!!!!

Answer 2

9x² + y² = 58
xy = 7 { given

we know (a+b)² = a²+b²+2ab
use it here

(3x)²+y² = 58
we can write it as
(3x+y)² - 2(3x)(y) = 58
put value of xy
=> (3x+y)² - 6(7) = 58
=(3x+y)² = 58+42
= (3x+y)² = 100
taking square root both side we get
3x+y = 10