Question

Dacă x=5 si a+b=13, calculati:
a) 3•x+7•a+7•b
b) x•a+x•b-50
c) 7•a-7•b+x=55
d) 13+x-(5•a-5•b)=2011

Answer 1

x=5  a+b=13
a) 3•x+7•a+7•b=3•x+7(a+b)=3•5+7•13=15+91=106
b) x•a+x•b-50=x(a+b)-50=5•13-50=65-50=15
c) 7•a-7•b+x=55
7(a-b)+x=55
a+b=13==>a=13-b
7(13-b-b)+x=55
7(13-2b)+5=55
7(13-2b)=50
13-2b=50/7
2b= -50/91
b=-25/91
a=13-b= 13+25/91=1208/91
d)13+x-(5•a-5•b)=2011
13+x-5(a-b)=2011
13+5-5(a-b)=2011
5(a-b)=2011-18
5(a-b)=1993
a-b=1993/5
a+b=13==>a=13-b
13-b-b=1993/5
13-2b=1993/5
-2b=1993/65
b=-1993/130
a=13-b=13+1993/130=3683/130