15х-у-2-14х=х-у-2 х=-16; у=-4
-16+4-2=-14
3ˣ⁺² + 9ˣ⁺¹ = 810
3² · 3ˣ + 9 · 3²ˣ = 810
9(3ˣ + 3²ˣ) = 810
3ˣ + 3²ˣ = 90
у = 3ˣ
у + у² - 90 = 0
у² + у - 90 = 0
D = 1² - 4 · 1 <span>· (-90) = 1 + 360 = 361; </span>√361 = 19
y₁ = (-1 - 19)/2 = -10
y₂ = (-1 + 19)/2 = 9
3ˣ = -10 - нет решений
3ˣ = 9
3ˣ = 3²
х = 2
cos47+cos73=2 cos(47+73)/2 * cos(73-47)/2=2cos60 * cos13=2*1/2*cos13=cos13