Question

(2x-5y)^2 = 4x^2 + 25y^2 - Kxy then K =​

Answer 1

(2x - 5y)^2

= (2x)^2 - 2.(2x).(5y) + (5y)^2

= 4x^2 - 20xy + 25y^2

compare this with the equation 4x^2 + 25y^2 - Kxy

we get the value of k = 20