Cos x = 1/29!/2!*7!log(4x+5) по основанию 1/3= -1

Question

Cos x = 1/2



9!/2!*7!


log(4x+5) по основанию 1/3= -1

Answer 1

cos x = 1/2
x = ± arccos(1/2) + 2pik
x = ± pi/3 + 2pik, k ∈Z

9!/2!*7! = (7! * 8 * 9 ) / (2 * 7!) =  (8*9)/2 = 72/2 = 36

log 1/3  (4x+5) = - 1
log 1/3  (4x+5) = log 1/3 (3)
ОДЗ
4x + 5>0
4x > - 5
x > - 1,25

4x +5 = 3
4x = 3 - 5
4x = - 2
x = - 1/2 = - 0,5 ==> удовлет ОДЗ

ОТВЕТ: - 0,5