Question

Докажите тождество (m^2-n^2)(m^2+n^2)-m^2 (m^2-n^2)-m^2n^2= -n^4

Answer 1

(m²-n²)(m²+n²) - m²(m²-n²) - m²n² = -n⁴
(m²)² - (n²)² - m⁴ + m²n² - m²n² = -n⁴
m⁴ - n⁴ - m⁴ + m²n² - m²n² = -n⁴
(m⁴ и - m⁴ сокращаем, как + m²n² и - m²n²)
- n⁴ = - n⁴
либо 
n⁴ = n⁴