Question

Daca a+b=3,2 si b+c=5,3, calculati:
a) 4a+5b+c
b) 2a+7b+5c
c) 3a+10b+7c
d) 10a+12b+2c

Answer 1

a+b+b+c=a+2b+c=8,5
a) 4a+5b+c=(a+2b+c)+(a+b)+2(a+b)=8,5+3,2+2×3,2=11,7+6,4=18,1

b) 2a+7b+5c=2(a+2b+c)+3(b+c)=2×8,5+3×5,3=17+15,9=32,9

c)3a+10b+7c=3(a+2b+c)+4(b+c)
=3×8,5+4×5,3=46,7

d) 10a+12b+2c=2(5a+6b+c)=2[(a+2b+c)+4(a+b)]=
=2×(8,5+4×3,2)=2×(8,5+12,8)=2×21,3=42,6