Question

If $3x+2y=12$ and $x=6$, find the value pf $9x^2+4y^2$.

Answer 1

Given $3x+2y=12...\left(1\right)$

& $x=6...\left(2\right)$

using eq (1) & (2) we get

$3\times 6+2y=12$

$2y=12-18=-6$

$[y=-3]$

now $x=6$ & $y=-3$

then $9x^2+4y^2=9\times (-6{)}^2+4(-3{)}^2$

$9x^2+4y^2=9\times 36+4\times 9$

$=36\left[10\right]$

$9x^2+4y^2=360.$