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=−9m⃗ +12n⃗ −10m⃗ +14n⃗ =−19m⃗ +26n⃗

3a⃗ +4b⃗ =3⋅(−3m⃗ +4n⃗ )+4⋅(5m⃗ −7n⃗ )=

=−9m⃗ +12n⃗ +20m⃗ −28n⃗ =11m⃗ −16n⃗

(3a⃗ −2b⃗ )⋅(3a⃗ +4b⃗ )=(−19m⃗ +26n⃗ )⋅(11m⃗ −16n⃗ )=

=−209m⃗ ⋅m⃗ +286n⃗ ⋅m⃗ +304m⃗ ⋅n⃗ −416n⃗ ⋅11n⃗ =
=−209|m⃗ |⋅|m⃗ |⋅cos0+590⋅|m⃗ |⋅|n⃗ |⋅cos4π3−416⋅|n⃗ |⋅|n⃗ |⋅cos0=

cos0=1 ; cos4π3=−12

Даны векторы a = –3m + 4n и b = 5m –7n, где |m| =2, |n| = 6,∠(m,n) =4π/3

Altry    1   06.11.2020 23:01    0