Question

Please explain,
Factorise 4x² + y² + 25z² + 4xy - 10yz - 20zx and hence find the value when x = -1, y = 2 and z = -3

Answer 1

Hey,

$4x {}^{2} + y {}^{2} + 25z {}^{2} + 4xy - 10yz - 20zx \\ \\ = (2x + y - 5z) {}^{2} \\ \\ = (2 \times - 1 + 2 - 5 \times - 3) {}^{2} \\ \\ = ( - 2 + 2 + 15) {}^{2} \\ \\ = 225$

Answer 2

x=-1
y=2
z=-3

putting the values in equation
4(-1)^2+(2)^2+26(-3)^2+4(-2)-10(-6)-20(3)
4+4+234-8+60-60
8+234-8
234 ans...