10%+20%= 30%
Ответ: цена товара понизилась на 30%.
1) 2m^2-6mn+5m^2+11mn=7m^2+5mn
2)8x^3+8xy^2-9x^3+9xy^2= 17xy^2-x^3
3)10b^4-15b^3-10b^4+15b^3=0
4)5x^3+6x^2+8x-8x-8x^2-4x^3=x^3-2x^2
а) 16х^4-81y^4=(4x^2-9y^2)(4x^2+9y^2)=(2x-3y)(2x+3y)(4x^2+9y^2)
б)48a^4-3b^4=3(4a^2-b^2)(4a^2+b^2)=3(2a-b)(2a+b)((4a^2+b^2)
в)1/81m^8-1=(1/9m^4-1)(1/9m^4+1)=(1/3m^2-1)(1/3m^2+1)((1/9m^4+1=(1/V3 m-1)(1/V3 m+1)(1/3m^2+1)((1/9m^4+1)
г)32-1\2 m^6=1/2(64-m^6)=1/2(8-m^3)(8+m^3)=1/2(2-m)(4+2m+m^2)(2+m)(4-2m+m^2)
Sin²x-cos²x=cos4x
-(cos²x-sin²x)=cos4x
-cos2x-cos4x=0
cos2x+cos4x=0
2cos(²ˣ⁺⁴ˣ/₂)cos(²ˣ⁻⁴ˣ/₂)=0
cos3x cos(-x)=0
cos3x cosx=0
a) cos3x=0
3x=π/2 + πn
x= π/6 + (πn)/3, n∈Z
б) сosx=0
x=π/2 + πn, n∈Z
Ответ: π/6 + (πn)/3, n∈Z;
π/2 + πn, n∈Z.