Question

factorise 25x2+4y2+9z2-20xy-12yz+30zx​

Answer 1

$\small \bold{(5x)^2 +(2y)^2 +(3z)^2−2(5x)(2y)+2(2y)(3z)−2(3z)(5x) }$

$\bold{=(5x−2y−3z)^2}$

Only x is negative.

$\bold{=(−(−5x+2y+3z))^2}$

$\bold{Or =(5x−2y−3z)^2}$