X-y=7
x^2+y^2=9-2xy
x^2+2xy+y^2=9
(x+y)^2=9
x-y=7
x+y=3
2x=10
x=5
y=-2
x-y=7
x+y=-3
2x=4
x=2
<span>y=-5
</span>
2a^2 - 3a + 1 - 7a^2 + 5a = - 5a^2 + 2a + 1
(sinx+sin3x)-(sin2x+sin4x)=0
2sin2xcosx-2sin3xcosx=0
2cosx*(sin2x-sin3x)=0
cosx=0⇒x=π/2+πn,n∈z
sin2x-sin3x=0
-2sin(x/2)cos(5x/2)=0
sin(x/2)=0⇒x/2=πk⇒x=2πk,k∈z
cos(5x/2)=0⇒5x/2=π/2+πm⇒x=π/5+2πm/5,m∈z