Question

a+b=7 b+c=11 calculează a+2b+c
a-c
3a+b+c
a+7b+2c
ab+ac+bb+bc

Answer 1

a+b=7 b+c=11 
a+2b+c=a+b+b+c=(a+b)+(b+c)=7+11=18
a=7-b
c=11-b
a-c=7-b-(11-b)=7-b-11+b=7-11=-4, deoarece -b+b sau b-b=0
3a+b+c=3a+11=3x(7-b)+11=21-3b+11=-3b+32
a+7b+2c=a+b+4b+2b+2c=(a+b)+2x(b+c)+4b=7+2x11+4b=7+22+4b=29+4b
ab+ac+bb+bc=a(b+c)+b(b+c)=(b+c)(a+b)=11x7=77