Question

Даны векторы a и b: |a|= 2, |b| =√2 , ∠(a;b) = 135°.
Найдите |а -2b|

Answer 1

(a-2b)²=|a-2b|²
(a-2b)²=a²-4ab+4b²=4-4*2*√2cos135°+4(√2)²=12+8√2*√2/2=20
|a-2b|²=20
|a-2b|=√20