Question

Помогите пж 81-(2х-5)^2
Формула :(a-b)^2=a^2+b^2-2•a•b

Answer 1

Формула: $\displaystyle \tt \bold{(a-b)^2=a^2-2ab+b^2}$

$\displaystyle \tt 81-(2x-5)^2=81-((2x)^2-2\cdot2x\cdot5+5^2)=81-(4x^2-20x+25)=81-4x^2+20x-25=56-4x^2+20x=\bold{-4x^2+20x+56}$