Question

Buna, am nevoie de ex 14,15 doar cele care le-am încercuit DAU COROANĂ ;)

Answer 1

14. a) x,y∈R

x²y-x(x-y)-x²(y-1)=xy

x²y-x²+xy-x²y+x²=xy

x²y-x²y-x²+x²+xy=xy

xy=xy (A)

b) Exista x∈R a, î:

x²-2x(x-3)+x(3-x)=3-2x²

x²-2x²+6x+3x-x²=3-2x²

-2x²+3x=3-2x²

3x=3

x=1 ∈ R => (A)

15.

3a+5b=20

5a+3b=8

a) 3a+5b=20 |•2 => 6a+10b=40

c) 3a+5b=20 |•3

5a+3b=8 |•5

=> 9a+15b=60

25a+15b=40

____________ -

-16a=20

a = -20/16 = -5/4 = -1,25

3×(-1,25)+5b=20

-3,75+5b=20

5b=20+3,75

5b=23,75

b=4,75

a+b= -1,25+4,75= 3,5