Question

Se dă a=3x-2y+1 ; b=-x+y-5 c=-3(x+y-4).Calculați:
a) a+b+c ;
b) 3a+2b-4c ;
c) -4(a+b)+5(-c) ;
d) ab ;
e) -ac ;
f) 2a-ab+bc .

Answer 1

a=3x-2y+1
b=-x+y-5
c=-3(x+y-4)=-3x-3y+12

a) a+b+c=(3x-2y+1)+(-x+y-5)+(-3x-3y+12)
3x-2y+1-x+y-5-3x-3y+12=2x-3x-y-3y-4+12=-x-4y+8.

b)3a+2b-4c=3(3x-2y+1)+2(-x+y-5)-4(-3x-3y+12)
=9x-6y+3-2x+2y-10+12x+12y-48=19x+8y-55.

c)-4(a+b)+5(-c)=-4(3x-2y+1)+5[-(-3x-3y+12)]
=-12x+8y-4+5(3x+3y-12)
=12x+8y-4+15x+15y-60
=27x+23y-64.

d)a·b=(3x-2y+1)(-x+y-5)=3x(-x+y-5)-2y(-x+y-5)+1(-x+y-5)
=-3x^2+3xy-15x+2xy-2y^2+10y-x+y-5
=3x^2-2y^2+5xy-16x+11y-5 (de aici nu mai pot continua)

Am incercat sa te ajut cum am putut. Sunt foarte obosita, dar sper ca mi-au iesit calculele. Sunt foarte multe subpuncte. Scuze!

Answer 2

e)(3x-2y+1)(-3(x+y-4)=(-3x+2y-1)(-3x-3y+12)=9x^2+9xy-36x-9xy-6y^2+24y+3x+3y+12=9x^2-6y^2-33x+27y+12
f)2(3x-2y+1)-(x-4y+8)+(-x+y-5)(-3(x+y-4))=6x-4y+2+4y-8+3x^2-3y^2+3x+27y-60=3x^2-3y^2+10x+27y-66