b₁ = 81 b₅ = 625 b₂ = ? b₃ = ? b₄ = ?
b₅ = b₁ * q⁴
q⁴ = b₅ : b₁ = 625 : 81 = (5/3)⁴
q₁ = 5/3 q₂ = - 5/3
1) b₂ = b₁ * q = 81 * 5/3 = 135
b₃ = b₂ * q = 135 * 5/3 = 225
b₄ = b₃ * q = 225 *5/3 = 375
2) b₂ = b₁ * q = 81 * (- 5/3) = - 135
b₃ = b₂ * q = - 135 * (- 5/3) = 225
b₄ = b₃ * q = 225 * (- 5/3) = - 375
Ответ : две прогрессии
1) 81 ; 135 ; 225 ; 375 ; 625
2) 81 ; - 135 ; 225 ; - 375 ; 625
Это разность кубов: а³-в³=(а-в)(а²+ав+в²)
Ответ: (7у²)³-1³=343у⁶-1.
7cos2x + 3sin^2(2x) = 3
7cos2x + 3sin^2(2x) - 3 = 0
7 cos(2x) - 3cos^(2x) = 0
cos(2x) * (3cos(2x-7)) = 0
1) cos2x = 0
2x = π/2 + πn, n∈Z
x= π/4 + (πn)/2, n∈Z
2) 3cos(2x) 7
cos(2x) = 7/3
2x = c0s^(-1)(7/3) + πk, k∈Z
x2 = 1/2cos^(-1) (7/3) + πk, k∈Z
2x = 2πm - cos^(-1)(7/3) + πm, m∈Z
x3 = πm - (1/2)*cos^(-1)(7/3), m∈Z
<span>2·2ˣ⁺² - 3·2ˣ⁺¹ - 5·2ˣ = -6
</span><span>2·4*2ˣ - 3·2*2ˣ - 5·2ˣ = -6
</span>8*2ˣ - 6*2ˣ - 5·2ˣ = -6
-3*2ˣ= -6
2ˣ=-6/-3
2ˣ=2
x=1
1) (3x - 7)cosx= 5cosx / cosx
3x-7 = 5
3x = 12
x=4 - первый корень
2) (3x-7)cosx = - 5cosx /cosx
3x-7 = -5
3x = 2
x = 2/3 - второй корень