Question

Cate exercitii vreti (macar 3)

Answer 1

1)x/5=y/7
7x=5y
x=5y/7

a)x+y=3
5y/7+y=3
(5y+7y)/7=3
12y=3·7
y=21/12=7/4
y=7/4
x=5y/7=(5x7/4)/7=35/4x7=25/28=5/4
x=5/4

b)y-x=5
y-5y/7=5
(7y-5y)/7=5
2y=7·5
y=35/2
x=5y/7=(5·35/2)/7=35/7=5
x=5

c)2x+3y=7
2(5y/7)+3y=7
10y/7+3y=7
(10y+21y)/7=7
31y=7·7
y=49/31
x=5y/7=(5·49/31)/7=245/31·7=245/217=simplif.cu 7=35/31
x=35/31

5)(x+2)/x=9/2
2(x+2)=9x
2x+4=9x
2x-9x=-4
-7x=-4       ·(-1)
x=4/7

6)x/(5-x)=3/7
7x=3(5-x)
7x=15-3x
7x+3x=15
10x=15
x=15/10
x=3/2