Question

Determine a e b na proporção a 7 quando:
_ = _
b 8

a) a+b=4
b)a+b=-5

Answer 1

a
a/b = 7/8
a + b = 4
( a + b)/a = ( 7 + 8)/7
4/a  = 15/7
15a = 7 * 4
15a = 28
a  = 28/15 ****
28/15 + b = 4/1
b = 4/1 - 28/15
b = ( 60 - 28)/15 = 32/15****

b
 a - b =  -5 ***
a/b = 7/8
( a - b)/a = ( 7 - 8 )/7
-5/a = -1/7
-1a = -35
1a = 35
a = 35 *****

35 - b = -5 
-b = -5 - 35
-b = -40
b = 40 ****