Question

factor comun:4+8+12+...............+400=
85a-5=

stiind ca :a+b=20 si c=5 calculati ac+bc

daca xy+xz=150si y+z=15 calculati cat este x

stiind ca:2*(a+3b)+3c=131,iar c+2b=19, aflati a.

Answer 1

4+8+12+.......+400=4*(1+2+3+.....+100)
$4* \frac{(100+1)*100}{2}=4*101*50=20200$
85a-5=5(17a-1)

a+b=20 si c=5
ac+bc=c*(a+b)=5*20=100

xy+xz=150 si y+z=15
x*(y+z)=150
x=150:15=10

2*(a+3b)+3c=131
c+2b=19
2a+6b+3c=131
6b+3c=131-2a simplifici cu 3
2b+c=$\frac{131-2a}{3}$
19=$\frac{131-2a}{3}$
131-2a=19*3=57
2a=74 deci a=37