Ex. 5 de la rezolva factorul comun si 3 de la rezolva exercitiile (ultimul ex. dupa pagina aceasta )

Dau coroana !

ex 3.
x + 2x + 3x + 4x +...+ 10x=385
x( 1+2+3+4+5+6+7+8+9+10)= 385
55x = 385 / :5
11x = 77/ :11
x= 7

ex 5.
a) ab + ac= 520
b+c= 52
a( b+c) =520
52a = 520
a= 10

b) ab - ac=45
b-c=9
a( b-c) =45
9a= 45/ :9
a=5

c)ab+ac+70=170
a=25
ab + ac= 100
a( b+c)=100
25 (b+c)=100/:25
b+c= 4

d) ab-ac-48=2
a=10
ab -ac=50
a(b-c)= 50
10 (b-c)= 50/:10
b-c= 5

a) ab + ac = 520  si b + c = 52
    a(b + c) = 520
    a * 52 = 520
    a = 520 : 52
    a = 10
b) ab - ac = 45 si b - c = 9
    a(b - c) = 45
    a * 9 = 45
    a = 45 : 9
    a = 5
c) ab + ac + 70 = 170 si  a = 25
    a(b + c) = 170 - 70
    25 * (b + c) = 100
    b + c = 100 : 25
    b + c = 4
d) ab - ac - 48 = 2 si a = 10
    a(b - c) = 48 + 2
    10 * (b - c) = 50
    b - c = 50 : 10
    b - c = 5 
3.
x + 2 * x + 3 * x + ..........+ 10 * x = 385
x(1 + 2 + 3 + ...... + 10) = 385
x * 10 * (10 + 1)/2 = 385
x * 11 * 5 = 385          | : 55
x = 7