7√25 (cos5π/8)^2-7√2(sin(5/8π)^2=7√2((1+cos(10/8π))/2-(1-cos(10/8π))/2)= =7√2(1+cos10π/8-1+cos10π/8)/2=7√2(2*cos5√π/4)/2=7√2*cos(π+π/4)= = -7√2cosπ/4 =-7√2*1/√2=-7. 5cos37°/sin53°=5cos(90°-53° ) /sin53°=5sin53° /sin53° =5. 24sin298° /sin62°=24sin(360°-62 ° )/sin62°= -24sin62°/sin62°=-24. 15tg15°*tg285°=15tg15°*tg(270°+15°)=15tg15°*ctg15°= 15*1=15. 18√6cos(17/4π*cosπ/6=18√6cos(4π+π/4)cosπ/6 =18√6cosπ/4cosπ/6=18√6*√2/2*√3/2=18*6/4=9*3=27.
Смотри решения во вложениях.
Решено с1 по 4, с 6 по 15.
(1/7+5/14)(4,5-7)
(2/14+5/14)*(-2,5)
7/14*(-2,5)
0,5*(-2,5)
-1,25
По теореме, обратной теореме Виета:
x₁ + x₂ = 12
x₁·x₂ = 2
x₁³ + x₂³ = (x₁ + x₂)(x₁² - x₁·x₂ + x₂²) = (x₁ + x₂)(x₁² + 2x₁·x₂ + x₂² - 3x₁·x₂) =
(x₁ + x₂)[(x₁ + x₂)² - 3x₁·x₂] = 12·(12² - 6) = 12(144 - 6) = 12·138 = 1656.
27а3+8b3-27a318a2b
+12ab2+18a2b+12ab2+8b3