7х-5х-3х-2х=-3х
ответ -3х
2(х+10)=7х
2х+20=7х
2х-7х=-20
-5х=-20
х=-20:(-5)
х=4
Скорость пешехода 4км/ч
Скорость велосипедиста 4+10=14км/ч
Проверка:2*14=7*4
28=28
Решение
<span>sin²x/4-cos²x/4=1/2
- (cos</span>²x/4 - sin²x/4) = 1/2
cos<span>²x/4 - sin²x/4 = - 1/2
</span>cos[2*(x/4)] = - 1/2
cosx/2 = - 1/2
x/2 = +-arccos(-1/2) + 2πk, k ∈ Z
x/2 = +- [π - arccos(1/2)] + 2πk, k ∈ Z
x/2 = +- [π - π/3<span>)] + 2πk, k ∈ Z
</span>x/2 = +- [2π/3<span>)] + 2πk, k ∈ Z
</span>x = +- [4π/3<span>)] + 4πk, k ∈ Z</span>