Question

Ajutor.Cineva ?
Multumesc.​

Answer 1

3a + 5b = 20

5a + 3b = 8

a) 5a + 3b = 8 | x2

=> 10a + 6b = 2 x 8

=> 10a + 6b = 16

b) 3a + 5b = 20 | x5

=> 15a + 25b = 5 x 20

=> 15a + 25b = 100

c) 3a + 5b = 20

5a + 3b = 8

---------------(+)

( 5a + 3a ) + ( 3b + 5b) = 20 + 8

=> 8a + 8b = 28

=> 8 (a + b) = 28 | :8

=> a+b = 28/8

=> a+b = 3,5

d) 3a + 5b = 20

5a + 3b = 8

---------------(-)

(5a - 3a) + (3b - 5b) = 8 - 20

=> 2a - 2b = -12

=> 2a - 2b = -12

=> 2 (a - b) = -12 | :2

=> a-b = -6

Answer 2

${3a + 5b = 20$

${5a + 3b = 8$

$= >$

${3a + 5b = 20$

{a=8/5-3/5b

$= >$

$3( \frac{8}{5} - \frac{3}{5} b) + 5b = 20 = > b = \frac{19}{4}$

$= > a = \frac{8}{5} - \frac{3}{5} \times \frac{19}{4} = > a = - \frac{5}{4 } = > (a.b) = ( - \frac{5}{4} . \frac{19}{4} )$

$a)10a + 6b = 10 \times ( - \frac{5}{4} ) + 6 \times ( \frac{19}{4} ) = - 5 \times \frac{5}{2} + 3 \times \frac{19}{2} = - \frac{25}{2} + \frac{57}{2} = 16.$

$b)15a + 25b = 15 \times ( - \frac{5}{4} ) + 25 \times \frac{19}{4} = - \frac{75}{4} + \frac{475}{4} = 100.$

$c)a + b = - \frac{5}{9} + \frac{19}{4} = \frac{ - 5 + 19}{4} = \frac{14}{4} = \frac{7}{2} .$

$d)a - b = - \frac{5}{4} - \frac{19}{4} = \frac{ - 5 - 19}{4} = \frac{ - 24}{4} = - \frac{24}{4} = - 6$