20 ! решите неравенство: 1) x^2+(m+1)x+m《0; 2) x^2-n^2/x-3> 0.

[tex]1) x^2+(m+1)x+m \leqslant 0 \\ x_{1} + x_{2} = - m - 1 \\ x_{1} \times x_{2} = m \\ x_{1} = - 1 \\ x_{2} = - m[/tex]

ответ: (-1; -m)

[tex]2) \frac{ {x}^{2} - {n}^{2} }{x -3}> 0 \\ [/tex]

х не равен 3

[tex] {x}^{2} - {n}^{2} > 0 \\ {x}^{2} > {n}^{2} \\x > n \\ x < - n[/tex]

ответ: х< -n; x> n

m(сплаве)=800g

ω(олова)=65%

ω(железа)=35%

m(железа)=35%/100%*800g=280g

cosa=-12/13

sina=sqrt(1-cos^2(a))=sqrt(1-144/169)=sqrt(25/169)=5/13   (знак + -2 четверть)

sinb=4/5

cosb=sqrt(1-sin^2(b))=sqrt(1-16/25)=sqrt(9/25)=-3/5 (знак - -вторая четверть)

cos(a+b)=cosa*cosb-sina*sinb=

(-12/13)*(-3//13)*(4/5)=(36//65)=21/65

cos(a-b)=cosa*cosb+sina*sinb=

(-12/13)*(3/5)+(5/13)*(4/5)=(36/65)+(15/65)=51/65